A good friend of mine here in Rawai who has lots of bikes and cars, will not rent out without a license, what should happen is when the police stop all these bike's at the road blocks, they should confiscate the bikes, and make the rental company come to the police station to collect the bikes with the rental contract, I think the police can fine the rental company for not taking a license, and also a IDP
The biggest culprits are these little shops buying a couple of bikes for rent, with them it's just about money,