A common problem with many cars you pick up in bulk lots, or on the cheap, is that they have been painted, usually badly, by a previous owner. You may want to strip it back to the original colour for show, or to increase its value, or you may want to just strip it back so you can repaint it yourself.
If the paint used is an enamel paint, its actually quite easy. Poorly applied and peeling paint can generally be wiped off with liberal amounts of Mineral turps, BUT NEVER use turps on clear plastic windows/screens!!! (as I learnt from bitter experience). In fact, as turps can soften some plastics, I prefer using a caustic type Oven Cleaner (the non-caustic type is safer for your hands, but is nowhere near effective). This will remove good or bad, thick or thin paint, eventually, off any type of plastic, including the clears window sections, and has never harmed any of the plastic bodies or components of the cars I have used it on (and I have used it often). Thinly applied and peeling paint will usually come off with a single application. Good quality paint that has been applied properly and has been on for years may take several applications. My best advice is patience! Its most effective on good paint if left on for a few hours, preferably overnight. Stubborn paint can also generally be wiped off with Mineral Turps once the Oven Cleaner has softened the paint (after one or two applications).