Alter the scenario a little bit. Instead of borrowing a vehicle, you had to go rent one instead. You would be out $50.00-$60.00-$70.00 for trunk rental. Does not matter if your plans changed. You would have the trunk overnight. The trunk would have a full tank of gas so you cannot count that.
THe family member, is not a jerk, will probably pay you for the gas you put in.
You are out the trunk and your time. If you feel like you want give him a refund, give him $50.00 and call it good. As others have noted, a deposit is a good faith offer. You took down your ad but if you had left it up you may have had another buyer on the line.