I have had a number of scammers trying to sell me equipment (digital backs) they did not own after I have placed ads on this and other sites....It is becoming very common. So here are a few tips....
1. Use Paypal for transaction, if you are a member, you usually qualify for Buyer Protection
2. Make sure you send money for "goods" or have seller send you an invoice for "goods"
3. Spell out any warranty return policy that seller agrees to on you paypal transaction message.
4. If paypal requires a 21-day hold, and is recommending seller provide delivery confirmation, and seller instead wants to wait out the 21-day hold, do not purchase.
5. Use escrow.com, which will cost you and/or seller a fee, but protects both of you. You receive item, and confirm it is as advertised, and funds are then released to seller.
6. If seller does not want to work with you on escrow.com, do not purchase.
7. Have seller placed dated piece of paper or tape on item, to make sure he has the item in his possession. I have had seller photoshop date on background, which proved he only had a photo to sell.....
Hope this helps