Just a word of warning... DO NOT BUY A CAR THAT IS "OWNED" BY A FINANCE COMPANY - unless you are in no hurry to get ownership.
I recently bought a car from a Thai woman. She had finance on the car, so I went with her to the large and reputable finance office to pay off her debt and then (I thought) get the Blue Book to enable me to transfer ownership to my name.
However, the finance company revealed - only after they had my money - that they don't have the Blue Book, it is somewhere in Bangkok (?) and they will get it for me in "2 or 3 days". It is now a week, and the finance company still doesn't know when the Blue Book will get here. In the meantime, the car has no current tax (another thing to check when buying), so I cannot renew the tax, and so have to rent a car if I want to drive and avoid potential legal calamities. So the car is costing me much more than the price I paid, aside from wasted time. Caveat Emptor, especially here in LoS.