What are tell tale signs that body panels are factory and not aftermarket, seems that allot of aftermarket is being sold as "OEM", fenders especially. Thanx for the help.........peace.

 

I would think a part# or id # is stamped in a oem part. However, most knockoff parts can usually be spotted by a poor fit. A cheap part is almost impossible to get the body lines to line up.
Another way is to look at surrounding parts that join with it. Lots of times, not all the holes/tabs, etc are there in the aftermarket part to accomodate the factory parts still in place