Basically, we had a lot of trouble staying away from scammers in Cambodia. It's not like we weren't careful. Most SE Asia countries see this phenomenon to a certain degree. For instance, in Bangkok, tuk tuk drivers offer to drive you around and then try to coherce clients into buying fake/cheap gemstones in jewlery shops where they have a commission. There are also many organised scams going on in Vietnam as well. Basically, when a smartly-dressed individual with more than basic english offers you help randomly, you should generally be cautious.
Knowing this, we have always been careful when travelling around here and have never had any issues (apart from paying a little too much for a cab ride from time to time). That all changed the minute we decided to cross the border into Cambodia. Now, it might have been the destination we chose (Siem Reap, the city where the famous Angkor Wat is located), or the border we crossed (Aranyapathet - Poi Pet) or maybe even the time of day (afternoon), but things quickly went from bad to worse.
First, we chose to cross the border independently. (Group crossings can be arranged in Khao San Road, but it's generally more expensive). We took an overland bus from Bangkok to Aranyapathet. The bus dropped us off in Aranyapathet on the thai side. Then, we had to take a tuk tuk from there to the border. Be wary, these tuk tuk drivers will bring you to an unofficial thai office where they will try and sell you a Cambodian visa. Don't purchase your visa at the thai office they bring you to. Instead, keep walking and go straight for the border crossing. You can arrange your visa directly there. The people at the thai office will try very hard to sell you a cambodian visa. I believe the visa they issue is valid, however they a lot more for it.(1200 baht). If you ask them, they will tell you it's the official way of getting the visa (it isn't). The people working there do not wear uniforms or any kind of identification. Truth is, you can get the cambodian visa directly during the border crossing for only 20$ (again, fair warning, if you pay in baht they will charge you more. It's 800 baht if I remember correctly).
We avoided the office and went straight for the crossing by foot. Right away, a well dressed man started following both my boyfriend and I and another couple. He kept giving us "useful advice" telling us where to go (which was indicated clearly enough) even though we kept telling him we were fine on our own (by then we were sensing he was trying to pull something fishy on us).
At the visa office, we got our visas with no issues in only a couple minutes. Keep in mind that you need a passeport photo for the visa. If like us the border officials tries to make your purchase the arrival card for 100 baht, refuse. The arrival cards are free at the next office. (at this point the guy from earlier was still following us despite our efforts to get rid of him. He even told us he "tried" to warn us not to pay the extra 100 baht. He obviously said this after we paid though.)
After the border crossing we got into a free shuttle for the tourist bus station from the border. This is apparently normal, or at least the Lonely Planet says it is the norm. (we reasearched the crossing beforehand to avoid any issues so we were expecting this). The man who was still following us encouraged us to do this (we should have been suspicious at this point) and even climbed aboard with us. It didn't seem that there were any other methods of transportation around though.
This shuttle brought us to the tourist bus station. There was no one there but a couple employee working at the ticket booths. When we inquired about bus schedules to Siem Reap, the lady at the bus station simply wouldn't answer us. This part we were already aware of. There is an organised scam going on from Poi Pet to Siem Reap. They force visitors to take a fixed price, two hour taxi to Siem Reap for 48$ US. This exorbitant fee is apparently standard and even endorsed by the police in Poi Pet. Since we had been forewarned, we weren't surprised to see that there was virtually no other options available and that the lady wouldn't cooperate and tell us bus schedules. She would probably have gotten into trouble if she had kept the taxi driver from getting us as his very lucrative clients.
With no other options, we managed to convice the other couple to split a cab with us for 12$ a piece. The trouble is, the cab driver and the men who had followed us all the way from the border kept asking to be paid the full amount up front. Our sources clearly warned about this. Do not pay the fare in advance. Apparently, most travelers that have paid before hand in the past never reached their destination and were dropped off in a random location by the taxi driver not long after he received his payment.
Of course, knowin this we refused to pay in advance to ensure we wouldn't suffer the same fate. However, our "guide" got very upset that we wouldn't. He started whinning and trying to convince us to pay right away. His argument was that if we didn't pay right away he wouldn't get anything in return for his work. (which basically consisted of following us even though we aked him not to). We tried to reason with him, but he wouldn't hear it until the man from the other couple gave him a bill of 10$ US so that he would leave us alone. At this point I was really starting to be pissed.
After we had to endure an horrible two hour drive with a mad men. First off he drove way too fast for our comfort. Second, he kept passing other drivers in the opposite lane which admitedly is quite common here in SE asia, but he was doing it quite carelessly, waiting until the last second before a collision to resume his own lane. Anyway, we were all relieved to still be alive once we got to Siem Reap.
Once in Siem Reap, the taxi driver was supposed to bring us all to our chosen hotels. Instead, he dropped us off near his tuk tuk friends who told us they would bring us for free. By then, it was dark and we were exhausted so we accepted even though we weren't convinced. Now you won't be surprised when I tell you that the tuk tuk didn't bring us to the right hotel. It was dark, we were on a small street in the middle of nowhere and we couldn't see the sign of the hotel so we weren't sure at first. We asked and everyone in the hotel's reception kept saying we were at the right place. Turns out we weren't, but we only discovered that the next morning. We also discovered that the tuk tuk drivers sleep there and regularly bring clients in pretending it's the hotel they wanted.
After we visited Angkor Wat, we left for Phnom Penh, already exhausted by the fact that we had to be constantly on our guard. Once we got there, we wanted to make our Vietnamese visa (the vietnamese visa needs to be arranged in advance) so we took a tuk tuk from the bus station to the Vietnamese embassy. The tuk tuk seemed fine at first, but then he started showing signs of increasing insistance towards us.
First, he decided to wait for us outside the embassy while we were arranging our visas (even though we said it wasn't necessary). He also tried to convice us to bring us to many other hotels that the one we wanted, but at least he didn't force us. After that, he tried to convince us to bring us to the killing fields. We told him we were leaving the next morning so we didn't have time and he started getting upset. He said he didn't have clients lately and that he really wanted to bring us. Then he tried to make us feel guilty for not visiting Phnom Penh, etc. Had this point we had had enough and thankfully we were in front of our guest house and we retreated quickly to our new room.
To make matters worse, the next morning when we went down to the bus downstairs, we saw that he was there trying yet again to tempt us into letting him bring us around. It was all quite creepy the way he wouldn't let go and wanted us to feel bad. We left Cambodia for Saigon and got through the border with no issues. We haven't had any issues with scams ever since even though there is apparently quite a few going on here in Vietnam.
So with all this said if you are still reading this (I probably lost most of you at this point!) here is my advice.
1) Any well-dressed individual that speaks good english and offers help (without being affiliated with a company you are dealing with such as a bus company) in Cambodia, Vietnam and Thailand (whether local OR foreigner) is probably not offering out of the kindness of his heart. These individuals should be treated with caution since they often work for organised scams.
2) Always be firm about your destination to tuk tuk and taxi drivers. Never pay in advance. Only pay once you have reached the exact destination you were going for. If the taxi doesn't have a meter, make sure to agree on the fixed rate before you get in.
3) If the tuk tuk fare is incredibly low, it's probably too good to be true.
4) Reasearch your destination before you go to avoid known scams or dodgy border crossings.
Hope this helped! Sorry if this is incredibly long, but I hope It'll be helpful to some of you if you are looking to cross overland from Bangkok to Cambodia.