Hi. Have a look at Toyota Sure. That's their second hand division. You will pay more but will have the guarantee its not financed, stolen etc. Looking at the tents sales, I've noticed so many vehicles having 60 to 80k kms on them, might be being too suspicious but I do wonder if they are being clocked. Check the tag on the seat belts. They have a manufacture date on them and are usually fitted within a tight timescale so is a good indication of when the vehicle was actually made.
Ii have the same visa. Did my first run to aranyaprathet. Was taken to one side by thai immigration on re entry and told I was only allowed 1 land border, next time I would have to fly. I asked why as I had a legit 1 year multi entry visa and did not get a reply. I know its the worst border but still makes no sense.
Asian Tigers handled my shipment and duty costs. Don't listen to people that haven't done this, they don't know. My advice would be use an agent, do not try and do it alone, customs will have your pants down. Downside is international shipping is expensive right now. Get quotes and do your sums first, se if it's worth it.