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 .