I didn't see any responses to the original post implying you thought anything untoward to the authors/publishers of TCR and the USCPG. I think we all agree they are great reference materials.

I have said this time and time again here. On eBay, it is caveat emptor. If a seller says something like "Accorrding to the USCPG, this chip is R-9 with a value of 500/1000/1500", and that very same seller has sold 10 of that very chip, one a week for 10 weeks, THAT SELLER IS DOING NOTHING IMPROPER as far as eBay is concerned. The guide says it. The seller has a right to say the guide says it.

Is it unethical? Yes. And if it was a club member doing it, he/she would have a problem. Outside of that, the seller is not misrepresenting anything. If the market has changed, it is the buyer's responsibility to figure that out. A seller sells, and anything the seller does to try and get a higher price on eBay without lying is fair game. That is the way eBay works.