I don’t think you can, at least not easily. Here’s a few things to consider:
- The price is too good to be true.
- The seller is claiming to be ‘selling on behalf of a friend’.
- The seller’s description indicates a lack of knowledge about the product.
- You do a search and find the same description and/or photos used in an older listing by a different seller and there’s no obvious connection between the two.
- You frequent forums and there’s a post by someone who has had their gear stolen.
A while back I was contacted by a person claiming to have legally purchased the contents of an abandoned storage unit, which happened to include Wilson Audio speakers and dCS digital gear, amongst others. He seemed fairly knowledgeable and his asking price for the items was consistently around Blue Book less 25%, so he appeared to have done research, if nothing else.
He seemed legitimate but it didn’t sit well so I passed on the deal. Some weeks later I saw where he had placed ads for the gear and someone had flagged them as stolen goods. I felt a little guilty for not being proactive in investigating him more thoroughly but also relieved at not having been scammed.