So, this is Thailand...and there seems to be a service for everything. I am about to purchase a used car from a private party and heard about the nightmares of waiting for 6+ hours to get the vehicle registered. I was thinking, I know that dealerships make copies of all documentation, bring the paperwork to the dept of land transport and register new vehicles for you. So why couldn't I find such a service to help me register my used car? Anyone have any experience with this?

Usually locals will do this all for you..

I know here on Phuket a fella will handle the lot for IIRC 600 baht.

Ask locally.

Check with places that offer driving instructions or that do vehicle inspections. A lot of them offer this kind of service.