Am I wrong about this? You seem to know a little more about it than I.
The main difference at point here is likely the precise way the trademark/registered trademark is used by the seller.
The law (
Lanham Act, for anyone interested) permits a non-owner of a registered trademark to make "fair use" or "nominative use" of a trademark under certain circumstances without obtaining permission from the mark's owner. The fair use and nominative use defenses are to help ensure that trademark owners do not prohibit the use of their marks when they are used for the purpose of description or identification.
So what you want to be able to do is DESCRIBE the items that you are selling, which is acceptable. If you went further, and used the mark in a way that implied a relationship between yourself and the mark owner, or that you were the mark holder, or applied the mark to products that were not from the mark holder, you'd be infringing.
For example, I can sell a Rolex watch on E-Bay under the username RJP, or on my own website called RJP-The-Watch-Guy.com and list something like "For sale: One Rolex Explorer II watch, brand new and unworn. (Note: I am not an authorized dealer or in any way affiliated with Rolex.)" and show a picture of the actual watch in question:
The above would be an adequate defense against trademark infringement as nominative "fair use" of the Rolex name, the Rolex logo on the watch itself, etc, because I am merely using the mark and information to describe a specific item I am selling.
However, if I listed the same thing on E-Bay with username "Rolex-Direct" or a similarly named website and said "For sale: One Rolex Explorer II watch, brand new and unworn." and then used stock art from the Rolex website for the photo (which is also copyright violation as well) - I'd be in trouble:
In doing it this second way, I am not describing
a specifc watch I am selling, but I am infringing upon the Rolex trademark by implying that I am
a seller of Rolex watches, authorized or otherwise.
There are other "gotcha's" you need to watch out for as well. For instance, look closely at the box - or ads - for this product...
...and you'll notice that the item in that box is not called "a Band-Aid" or "Band-Aids" but rather they are always properly refered to as "Band-Aid brand adhesive bandages."
If you are selling a box of these things - whether you're an authorized seller or not - and you advertise them as "Band-Aids" it is not unlikely that you'll get a call from a lawyer in New Brunswick, NJ pretty soon. (I can give you his name and direct dial extension if you like.)
Clients like J&J spend billions of dollars to establish their brands and trademarks; they go to great lengths themselves to ensure they don't violate or dilute their own intellectual property...they certainly need to ensure that no-one else does either.