Thats the worst part. Its one thing if you have a wrecked car from an auction thats dead nut stock and your repairing, but if its a customized car your repairing or in this case building you have better looked that car over very good. Chances are very good it could have a junkyard motor swapped in, trans, doors, etc. that you didnt know about when you bought it. Or, you swapped them and never thought you would need to do this type of inspection and didnt keep your records. And they have every right to detain the car on the spot for suspect stolen parts, even if they wernt stolen and were on the car when you bought it you dont have recipts showing that then they are considered stolen.