Finally checked out Pioneer Auto Sales (Lawton, OK) after seeing their lot on my commute for months. They keep around 32 vehicles, mostly in-house financing (buy-here-pay-here). They were totally fine with my mechanic doing a once-over, which honestly settles half the trust question.
Lot address: 2576 Credit Row, Lawton, OK. Visitor parking: Front-lot customer stalls facing the office; overflow on the side street near Lawton lot gate.
Paper side: licensed with the state (looked it up), about 97% of stock has title in hand per the office, and they offer a 30-day/1,000-mile powertrain warranty.
Overall: good people to deal with. 11 years in business around in-house financing (buy-here-pay-here), doc fee $299 and it's on the window sheet, no games. I'd send a family member there.