If at all possible, obtain your customer's phone number.  This may be helpful to avoid unanswered email when trying to close a deal.

Obtain references your customer has done business with.  When making deals that involve a lot of money, this is always a good idea.

Consider small transactions with new customers first.  This may be helpful before you give up that high priced memorabilia item.

Reference bad trader lists (black lists) before finalizing a deal.   It is a good idea to bookmark bad trader lists for future reference.

Consider utilizing a neutral party to finalize a deal.  For example, Both parties send their merchandise to a neutral party who then  distributes the item(s) to the appropriate parties.

Be alert when conducting business with customers utilizing free email service.  These email providers do not limit the number of accounts a person can have - making it easy for someone to change their identity.  Sports Memorabilia Online utilizes a free email provider (Hotmail) for two reasons: (1) so our staff can conduct business from multiple remote locations and (2) this service reduces our overhead cost, enabling us to offer our products at competitive prices and keep our services free.

Also, be alert sending merchandise to P.O. boxes.  Although P.O. boxes do cost money and these are the only means for mail in rural reas, there still is a changing of identity issue.