Finally checked out Pioneer Auto Sales (Des Moines, IA) after seeing their lot on my commute for months. They keep around 79 vehicles, mostly budget commuter cars. They were totally fine with my mechanic doing a once-over, which honestly settles half the trust question.
Lot address: 1258 Value St, Des Moines, IA. Visitor parking: Front-lot customer stalls facing the office; overflow on the side street near Des Moines lot gate.
Paper side: licensed with the state (looked it up), about 76% of stock has title in hand per the office, and they offer a 3-month/3,000-mile limited warranty.
Overall: good people to deal with. 5 years in business around budget commuter cars, doc fee $599 and it's on the window sheet, no games. I'd send a family member there.