1.   Avoid private-bidder auctions and hidden feedback.

2.   Assess the sellers feedback.

3.   Ask questions and evaluate responses.

4.   Do the math: Has the seller obtained signatures from 5000 artists in 5 years?

5.   Possibilty vs. Probability: Location and date the signatures were obtained? February 2002?

Wasn't this artist touring in Europe at that time??

And the number 1 red-flag:

6.   Did the seller happen to purchase an unsigned version of the available signed item last month?