In Germany I'd go directly for the manufacturers websites. They have a dedicated offer for "approved" used cars that come with warranties and such, and went through QA after being returned.
Jaguar Land Rover is pretty decent, they offer two year warranty. Prices are OK, if you have time to shop around or wait, since the value loss is, for whatever reason, higher than comparative German Premium brands. Service costs are reasonable as well (compared to Ford, Peugeot and free garages). You basically get a lot of car for your buck, plus you don't see those a dozen time between ypurbplace and the supermarket every day.
One heads-up so: Jaguar Land Rover dealerships are independent (some kind of frnachise system would be my guess), so experience can, and does, vary a lot between dealerships.
Another source would be exihibition cars and those registered for a single day (done to drive numbers, so propably not a thing at the moment, I haven't checked in a while).
Asking for a leasing return cars at ypur local brand dealership for sure is an option as well.