1) The person you borrowed from has no right to pass interest, fees, etc. onto you unless you had agreed to them--so if he had told, for example, prior to you borrowing the money that he would do  this and you agreed to borrow it anyway, that would be legal.2) He would have no right to repossess the car unless you specifically gave him a security interest the car (used it as collateral). Since you apparently did, he would have the right to repossess the car. He could also sue you for any balance due if the car is not worth enough to satisfy the loan--for example, if you still have a remaining balance of $9,500 and the car's current blue book value is $8,500 at the time you default and he repossesses, he could sue you for the extra $1,000.