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).
A few words of warning though: -Strip off all chrome or other painted components you don't want stripped. The oven cleaner will remove all enamel based paints or substances. It should be OK on most tampo printing, but I'd be very cautious with those and test it out on an unseen section or unwanted body first.
Its hard on your hands, so either use gloves or wash thoroughly afterwards.
You can wipe the oven cleaner off (a rough surfaced rag or nonmetallic scourer work well), but I generally find it just as effective and less messy to wash the softened paint and Oven Cleaner off using a toothbrush and hot soapy water. (Do this in the laundry or preferably outside, or you'll get into BIG trouble with "she who must be obeyed"! - And don't use a good toothbrush for the same reason!) BTW - The tooth brush lets you get into little corners and embossed/mesh/grill sections.
If you want to repaint the car, the oven cleaner NEEDS to be COMPLETELY remove from all surfaces of the car, as it will repel the paint. After thoroughly washing the car, I usually find it a good precaution to wipe the car over with a little mineral turps and dry it thoroughly just before painting.
So, what do you do if the paint is a plastic based paint (I hear you ask)? Not much is the short answer. I did strip a plastic based paint once, but it took me days of sanding to get it off, and the plastic lost its shine, and some of the detail. I was going to try a plastic paint stripper, but was told that will affect the plastic body, so I don't know whether or not that is an alternative. The moral to this story is that if you want to paint a slot car, with the intention of maybe stripping it back eventually for any reason, don't use plastic paints.
I have also been asked what sort of paints I use, as many people have been impressed with my paint jobs. I use whatever enamel based spray paint I can find that has the colour I want. Cheap stuff seems to do almost as good a job as the dearer stuff, the main difference I usually find is in the gloss level. The better quality paints usually give a glossier finish.