I took the afternoon train more than once. You need to be fast in getting or joining one of the few songtaews at the train station. Motorbike taxis are also few. No wait at the Thai checkpoint. Similarly, no hassle in getting a Cambodian visa. They will ask for 5 USD extra which would be still less than the cost for an electronic visa. You can stay your ground and stick to the real price but it will take a bit of time.
No problems with getting a camry. You will be offered transport even before reaching the Cambodian passport control.
The trick is to pay only on arrival in SR and that at the point you want. If you do not have too much to carry I would suggest that you pick a drop-off nearby the hotel but not exactly at the place. The driver might try to extort a commission from the hotel.
Do not pay more than the usual rate, not late fees etc. I would not talk to touts in any way and ignore them. Just go to the driver by walking a circuit. Meaning: turn left when leaving the passport control. Go around the roundabout to the cars. If you walk straight, some tout will get a few dollars by walking next to you and claiming that he delivered you. That money would come from your wallet.