Comments for eBay adds a "Comments"-Tab to any eBay-Item page that you visit. You can thus talk to others about the item for sale, the seller, ask questions, and tell fellow eBayers when you found the item somewhere else for less.
You discover a fake item (watch, handbag, shoes, etc.)?
Let others know so they don't make the mistake of buying it, believing that it is the real deal!
You discover the same product on a different site for much less?
Don't let others pay too much, let them know where to get the item for a cheaper price.
You notice that the seller is artificially pushing the price of the item by bidding with a second account?
Let others know, so that they don't get fooled into paying a price that's much too high!
You have a question that others can answer better than the seller of the item?
Post your question as a comment and let others help you out!
The add-on works on any of the eBay Country-sites and automatically adapts to the local language.