1. Before you bid, contact the seller with any questions you
    have.
  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
    policies.
  5. Determine the shipping charges before you buy.
  6. Be wary if the seller only accepts wire transfers or
    cash.
  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