Mostly (95%) are gracious and are interested in the information. I find the best way to approach the seller is gently, without accusing them of mis-representing, since they themselves may know nothing about beads and were sold the beads under false pretexts. I also try to provide links to other eBay auctions selling the same beads with the proper id, or direct them to BCN for discussion about their beads and suggest they post them.

5% of the time the response is angry and defiant. My favorite outraged response concerned "first century Islamic beads" and the seller refused to acknowledge the fact that the Prophet was not born until the 6th century. A few times the seller insisted that a "bead expert" had certified their beads as authentic. Then they would not identify the expert.

And once, the seller was extremely irate and retaliated by winning one of my $9 auctions then posted bad feedback, which I had to protest to eBay.

So, be aware that your helpful message may be interfering with someone's attempt to profit (sometimes a great deal) from the mis-representation and ignite a backlash that you may not enjoy dealing with. I don't contact many sellers these days, and do so very carefully, when they have made a glaring error that I just can't ignore.