you should not be able to buy any car with HP on it,unless you are buying it from a friend or a cowboy dealer,dealers are,by law not allowed to sell any car with outstanding hp on it,it must be paid off, its different if the car is bought by a loan,but answering your question,the person whos name is on the HP is responsible for all the payments,if payments are not paid,ie you buy the car from a friend and he does not pay,the car can be snatched back,by the HP company