Car purchase

The certificate of residence doesn't really mean that you need to "prove" residency as it may seem. This had me freaked out when I ordered my Tesla last month. You just go to Immigration with the TM.18 which is the application for certificate of residence and 3 passport photos. You can check off on their forms they give you that you want it for both purchasing a car and obtaining a license and they will give you 2 certificates, if you happen to want to get your driver's license here. You only need to if you stay for 6 months or longer at a time. I recommend it if your home country license doesn't have authorization to drive a motorbike and you might drive one here. I recommend you look up online everything that you need to bring when you apply, by the way. And if possible, print the TM.18 already filled out to save some hassle.

As for the registration, for a new car the dealer should be registering it for you and that's what this certificate is for so they can bring it down there and take care of it. I can't say whether they'll deliver the car to you or not; I'm going to Bangkok to pick up my new car next Monday and all I know is Tesla doesn't deliver to Pattaya but who knows with other dealers / makes.

Great info. Would this apply to used cars as well? I would think that some of these car dealers know how to circumvent the process 

That's going to depend on the dealer, I'd imagine. Some might do the full service for you and others might leave you on your own.