I did some searching online and couldn't come up with much of anything on Bar None except their own web site. By reading through their site, they specialize in obtaining financing for those that cannot go through the traditional methods (banks, credit unions, car financing arms). You will absolutely pay the highest APR through someone like Bar None...
The one quote I saw should give you some idea of the fact that they WILL charge pretty high rates and some even higher depending on credit history:
"The degree of past problems in conjunction with the current circumstances will determine details such as interest rates, down payment requirements, payment qualification and term of the loan, to name a few."
I believe, that based on the info on their site, that they only work with specific dealerships that have arrangements with them. I would guess that these are not the major dealers in your area, but are ones that specialize in the high-credit risk that Bar None works with.
Their site (which you probably already have)
Bar None FAQ'sI would recommend, that unless you have no other options, you stay away from these types of loans as you will pay through the nose and end up paying twice (if not more) than what the car is worth.