The irony of the Visa On Arrival lane is that if you use the normal line, sometimes they ask to see things like return air ticket, hotel reservations, etc... and (rarely) evidence of cash.

When I use the priority lane which is open to everyone for an extra 200bht fee, I've never been asked. It's as if they assume that anyone willing to pay the extra $7 usd (equivalent) is obviously an upstanding citizen.