A dealer in my area makes high end custom tube amps, many employing very valuable vintage parts. Recently, I saw a listing of Western Electric 171C output transformers, a part he frequently uses, at a very nice price. The seller claims that he pulled the transformers from Western Electric 124 amps. When my dealer asked whether he would allow a return if the part turned out not to be genuine, he was told that there was no assurance that the part was genuine (how could it be otherwise if it was pulled from a 124 amp?). My dealer also asked, and got no response to the question of why would someone pull the transformers to sell them separately from an amp that would sell for ten times the price he was asking for the transformers. This dealer has nerves of steel when it comes to buying parts. He recently bought a pair of input transformers for a custom build that cost $10k for the pair; it came from Japan so he felt more confident about it being genuine than a similar pair offered from a Chinese source.
As a seller, he often gets scammed by buyers. A common scam involves a sale of vintage tubes. The buyer claims that the tubes that he sent are defective and insists on returning the tubes for a refund. When the tubes come back, they are not the same tubes that were sent.