Never been asked, and never have more than about 20 GBp when flying in - just go to the ATM and get Baht as and when. Came in without a visa last year - asked for a 30 day visa on arrival, asked for address - "It's on the card" OK.. Very helpful. said go to Nakon Phanom and the lady there will give you an extension - which she did, then went over to Laos and got a years visa. I have always found the Immigration to be helpful, be polite and tell the truth. NP IO - because I live in their area.