Ok I worked at one of these paces and here's it works.
Your rate will be the highest legal amout they can charge you, about 20-25%
There will be an acceptance fee of $500 - 1500 (don't worry they roll that into the note)
They will more than likely tell you to qualify you need to buy an extended warrenty for $800-2000 that will cover one year and 15,00 miles (again rolled into the note)
The car will be sold at FULL RETAIL of book and typically it will be an undesirible car (ones that never sell for full book)
The term is typically only 2 years but you end up paying any where from 30-60% depoending on the car.
Also if you are ONE DAY late they can come get your car.
If you have such bad credit that you need to use a place I would suggest saving up 300 and buying a metro.