When buying a Tourist Visa at the Cambodia Visa office, the police officers will draw your attention to a hand written note saying that there is an additional fee of 100 Baht to be paid to issue a Visa.
This is a complete scam. The fee for a 30 Day Tourist Visa is currently US$30 (NOT a Cent or a BAHT more !).
I politely refused to pay this additional request for 100 Baht. Naturally, the police officer drew my attention to the "unofficial" hand written note, so I said OK, I would like a RECEIPT please. After some discussion between the officers, my Tourist Visa was rather grudgingly issued without paying the additional 100 Baht.
This is one of the many scams practised at Poipet and refusal to pay may cause a rethink. I would advise travellers to stand their ground on this. The other trick played is that you have to wait a bit longer to get your Visa if you refuse to pay the 100 Baht fee, so trying to justify the fee for a somewhat "express / fast track" issuing service.
The sheer excessive number of police officers at the Visa office astounded me, suggesting that many are benefiting from this racket.