"Spot delivery" is a technique where a Buy Here Pay Here dealer may let you drive the car off the lot before you're officially approved for financing, then calls back and demands more money or says you need to renegotiate the loan. To protect yourself, don't take the car until you are fully approved, and keep track of all your paperwork and everyone you speak with. Do not park the car at the dealer should you return, since the Buy Here Pay Here dealer could lock you in and repossess your car. Bring a witness with you for your buy here pay here dealings to serve as an advocate, and consult a lawyer if you suspect you're being scammed.
In your search for an auto loan, you may have considered a Buy Here Pay Here dealership; an auto dealer that essentially acts as a bank by offering loans in-house to buyers with bad credit. These buy here pay here dealers can offer an alternative to the traditional route of securing an auto loan, but they can also be trouble if you don't know what you're getting into.