between covid extension and some bavk and forth on visa waiver 30 days I ended up at the Cambodian border trying to get in on a visa waiver
last week with 175 days spent in thailand over the last 12 months.
been pulled aside and grilled by immigration. ( I had over 20k in cash , flight out of Thailand 3 weeks later , proof I had income coming from oversea . that wasnot enough.
thankfully I managed to get a copy my thai marriage certificate otherwise I would have been sent back to Cambodia. and they let me in but been told to get a non 0 ASAP...
if you have spent less than 180 minus 45 days ( 135 days ) in thailand over the course of the last 12 months there won't be any issue . they might ask for your return ticket which has to be no later than 45 days after your arrival date .
shall a 30 days extension put you over the 180 days limit the extension might be denied and you would be given at best a 7 days extension to put your affairs in order and leave the country .
this is from my personal experience having a lchat with an immigration officer at the border .