When I picked up the IJ, the seller did not trust the bills (I just picked those up from the bank). One by one he held them up the light checked both sides and complained that most bills were new unused bills (he said he never saw these ones before). He did that several times for the whole stack and finally after 30 minutes he was satisfied that they were real bills.
I think the saying goes like "Ill doers are ill deemers"