I have done it. You just have to avoid talking to the scammers that want to help you where the buses stop. Just walk right to border border. If you have prepared a evisa its easy to just turn and go back once they stamped you in at the Cambodia side
one option for extension is proof of income in the form of monthly payments to your Thai account of 65.000 THB or more. That money doesn't need to sit in the account and can be used as they are coming.
Start coming on 60 d visa extemption or a non o retirement. Start transferring 65k THB per month to a Thai account in your name. That 65*12 is used for extension next year. You can spend all of that if you want.