How can I be certain that a seller’s Second Chance Offer is legitimate?
A seller can send a Second Chance Offer to any of the non-winning bidders if the winning bidder does not pay the seller, if a seller has duplicate items, or the reserve price is not met in a Reserve Price Auction.

To make sure a Second Chance Offer is legitimate: Click My eBay at the top of the eBay Home page.
Sign in and look for the Second Chance Offer in My Messages.
Legitimate Second Chance Offers are forwarded directly from eBay and appear in My Messages with a green background and subject stating, “You have a second chance offer."
Note: eBay will never send a Second Chance Offer email with the subject line "Question from eBay Member." If you receive an email pretending to be a Second Chance Offer with that subject line, please report it to eBay. You can report this type of email from the Misuse of the Contact an eBay Member page.