After buying and selling stamps on Ebay for over 12 years, I have seen many sellers come and go. Some very good and some not so good. And, during that time I have compiled a list of things I feel prospective buyers should be aware of when deciding whether or not to place a bid for a particular stamp. Of course, these are just general observations and may not apply to all sellers but I feel that they provide a pretty good outline of things one should be on the lookout for. In no particular order, I would avoid sellers....

** That offer a picture of the stamp being offered that is smaller than your pinky nail. You would be surprised at how many of these I see offered. How can a prospective bidder possible make an intelligent decision on whether to bid on something they cannot see.

** That offer a picture that is so out of focus that it looks like a bowl of wet corn flakes. Again, how can you bid on something where you cannot accurately judge the quality or centering. You might as well try throwing darts through the eye of a needle.

** That offer the disclaimer "I am not a stamp expert but...". All I can say is beware.

** That offer their stamp(s) on an "as is" basis. Who knows what's lurking on the side you cannot see.

** That do not allow you to send your purchase for expertization. That is, they will not provide a refund is the stamp comes back as anything other than genuine (and it was described as completely genuine).

** That have a feedback rating of less than 92%. You may want to do a little research as to why the seller has so many complaints.

** That state in their listing "I am offering this on behalf of a friend..."

** That state "looks like real gum but it may be regummed" in their description and then state the catalog value as if it had original gum.

** That state that a particular stamp is "Mint" in the title of the listing but in the description they call the stamp regummed. This tends to lead inexperienced
    bidders to believe that the particular stamps' value is greater than it actually is. I have seen, on more than one occasion, where a particularly
    wide-known seller does this. If you are not already aware, a regummed unused stamp is usually worth about half (or less) the value of a stamp that
    has its original gum (Mint).

I know that there are more signals and I will add to this list as I discover them. But, as I state with my other guides, educate yourself. It's your best defense against sellers that either don't know what they're selling or worse - those that know what they are selling but hope that you don't.