1. Before you bid, contact the seller with any questions you
  2. Review the seller’s feedback.
  3. Be cautious when dealing with individuals outside of your
    own country.
  4. Ensure you understand refund, return, and warranty
  5. Determine the shipping charges before you buy.
  6. Be wary if the seller only accepts wire transfers or
  7. If an escrow service is used, ensure it is legitimate.
  8. Consider insuring your item.
  9. Be cautious of unsolicited offers.

Source: IC3.gov