Swung by Horizon Auto Mart in Des Moines over the weekend since a few people here asked about them. They keep around 52 vehicles, mostly family SUVs and sedans. They were totally fine with my mechanic doing a once-over, which honestly settles half the trust question.
Lot address: 5521 Family Plaza, 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 100% of stock has title in hand per the office, and they offer a 30-day/1,000-mile powertrain warranty.
Overall: mixed feelings. Cars looked right but I got two different answers on a title question, and that's my personal tripwire. If you go, get the title status in writing before any deposit.