@Steve *******
brings up an excellent point
Remember people ANYTIME you're stamping in to the country on a visa exempt/waiver/tourist visa entry you can be asked for the 3 proofs (AND that you have never been asked doesn't mean there isn't a rule about it on the books)
Those are
proof of funds 20K baht or the equivalent in CASH
proof of onward travel in the number of days you'll be stamped in for
proof of lodging (usually for a couple days BUT can be for the whole time)
Using a service to bounce out and back you won't need to worry about those things (unless you're told to by them) but going it alone you could be asked AND could be denied entry IF you are asked you don't have one of those 3 things