Buy here pay here ain't no joke. My uncle is setting up a BHPH dealer right now and will probably make a good bit of money if he does it right.
People with bad credit need cars too.
If you have the capability to own one or start one up, I'd say go for it. There is a demographic that will always be there to cater. I'd venture to say that MOST of the people will make the payments on time and it'll be fairly stress free. But the ones that do cause you problems, they will definitely be that headache.
I remember a fairly well to do person said that the best money making investment he had were trailer parks, because there was always that demographic looking for cheap places to live. Makes sense.