I meant it to be a suggestion to what might have actually happened. The threadstarter miscalculated his own entry stamp by one day. I am just proposing that something similar could have happened to you as well. You would not be the first person who is misinterpreting the entry stamp. The duration of a visa validity never is the same as the duration of the stay permit granted.
There can only be ONE explanation: I guess you had miscalculated your stay by one day (like the threadstarter!) and you were already in overstay, since they pulled you aside after you already stamped out, which is the usual routine on overstayers. And for overstays less than 24 hours the 500.- THB fine normally gets waived
WHO would have stopped you after you had already exited through Immigration at the airport at 10 pm? Once you exited through passport control and Immigration, before midnight, you weren't in any overstay. WHO spoke to you in the International Gates area?
May 1st thru June 29th, that's exactly 60 days. The day of entry counts as number one, and the last day counts until midnight. Just repeat the count on your calendar - it's exactly 60 days
he was wrong, you don't need 800,000.- THB in your thai bank account for the Non-Imm-O marriage visa. 400.000.- THB are sufficient. 800.000.- THB are only required if you intend to change visa type to a "retirement Non-Imm-O visa"
"re-enter when your Non-O has expired" . .sorry, it should say "when your Non-O/A has expired". As long as the Non-O/A is withinm the first year visa validity, there is no way to invalidate the stay permit that was granted based on the Non-O/A visa. He needs to await the expiry of the Non-O/A visa validity and put 400,000.- (not 800.000.-) into a Thai bank account, in order to apply for the change of visa type on immigration from a visa exempt entry to a "90-days Non-Imm-O family visa" (which requires proof of marriage and 400,000.- THB in his account)