I experienced already before a "mistake" of a sales-woman in a shop in giving back money in the case of paying with a 1.000 Baht note. The banknote disappears in the cash-register and the money paid back is as one has given a 500 Baht note. Afterwards no prove is there anymore. Might be it happened already several times to me because sometimes I don't check careful enough. Last night the same again in a very well known bar in Bangkok with two sister bars in Bangkok and Pattaya. The same "mistake" and I was lost because the management was not very diplomatic saying that these are often made mistakes by the client and his staff does not cheat (I was not mentioning this): "see, the paid amount is showing at the slip, so you paid with 500 Baht". Furthermore there were right away 4 waitresses around to testify that I gave only 500 Baht......... Do you have (had) problems in paying with 1.000 Baht??