I am going to Cambodia for 6 months on an ordinary visa. During that time I may want to visit Thailand 2-3 times for about a week each time, for shopping or medical services. Can I do this on a visa waiver or do I have to expect trouble from the 2nd time on?

You will not have a problem.

You will not fit the profile of a in/out visa runner.

you should have no problem.

Thank you both

Yes, no problems.

However, my Vietnamese friend who I picked up on the Thai-Cambodia border at Hat Lek/Cham Yeam (Koh Kong) a few weeks ago was first asked by Cambodian immigration to request "permission" from the Thai immigration authorities before they would stamp him out. The Thais happily let him in, but his outbound air ticket and my letter stating he would be residing with me (in the end he only spent one night at my place as the other two nights we were travelling) helped - I think he was asked for sufficient funds or an air ticket - he had only an air ticket but wouldn't have had 20,000 or even 10,000 Baht to show, only maybe 5000. However, that's because he's Vietnamese that he was targeted and subject to more scrutiny as that is one of the target nationalities of the crackdown. Never-mind the fact that my friend has only ever stayed in Thailand for a few days at a time, hasn't been here for 7 months and always comes here in my presence; there has never been a reason for him to travel here alone unless I'm here too as we do business together so that means every single time he has ever been to Thailand was with me.

Thank you for this interesting story which shows me that my initial worries were not completely unfounded. I am not Vietnamese, but I think the personal preferences of an immigration officer can hit just anyone. I'll carry a return ticket and enough money so I'm probably safe, but I am still curious to see what happens.

Yes, no problems.

However, my Vietnamese friend who I picked up on the Thai-Cambodia border at Hat Lek/Cham Yeam (Koh Kong) a few weeks ago was first asked by Cambodian immigration to request "permission" from the Thai immigration authorities before they would stamp him out. The Thais happily let him in, but his outbound air ticket and my letter stating he would be residing with me (in the end he only spent one night at my place as the other two nights we were travelling) helped - I think he was asked for sufficient funds or an air ticket - he had only an air ticket but wouldn't have had 20,000 or even 10,000 Baht to show, only maybe 5000. However, that's because he's Vietnamese that he was targeted and subject to more scrutiny as that is one of the target nationalities of the crackdown. Never-mind the fact that my friend has only ever stayed in Thailand for a few days at a time, hasn't been here for 7 months and always comes here in my presence; there has never been a reason for him to travel here alone unless I'm here too as we do business together so that means every single time he has ever been to Thailand was with me.