Can I enter Thailand on a visa exemption before using my SETV?

My impression is that it will work if they miss the visa, if they see the visa you will get stamped in on that. I asked once myself, as I was only in Thailand for 48 hours to get a flight somewhere else and then was coming back, and they insisted on stamping me in on the visa. I'd say your best *chance* is not writing the visa number on the arrival card and just hoping they miss it. The IO did go off to ask for me, though, if I could have a visa exempt entry, so it may depend on who you get like Tod suggests.