First, why am I writing this guide?  I am writing it because I just read a guide that suggested buyers should Opt Out of receiving second chance offers.  The persons reasoning was there are two many scams on eBay relative to second chance offers.  I disagree and her is how you can protect yourself.

1. Check your eBay messages to be sure the offer came from eBay.
2. Make sure it is an item you bid on.
3. Ask the seller why the item is available - if it was a return - pass on the offer.
4. Check the sellers feedback - not just their score but the actual comments.
5. If you are paying by PayPal and the item is protected with PayPal's buyer protection policy - you have very little risk.
6. You have no more risk with a second chance offer than you would have had if you were the original buyer.

Why second chance offers are good for sellers.  If the person who won the item did not pay - the seller has a second chance to sell his item and not lose his eBay fees.  Certainly the seller can re-list the item but even if it sells, the seller will only recover his insertion fee - the lowest portion of the cost of an auction.  In the case where a seller has multiple items, it allows him to sell more items at a lower cost (also lower profit).

Why second chance offers are good for buyers.  It allows you to purchase an item that you wanted at the price you were willing to pay.  Second chance offers from reliable sellers carry no more risk than if you were the original buyer.  You checked the buyers reputation before you bid the first time and it probably has not changed - check it again to be sure. 

I hope this helps someone who might have been encouraged to Opt Out of second chance offers.  They are good for both the buyer and the seller.  Don't let FEAR (False Expectations Appearing Real) keep you from getting something you want!

Best of luck with all your eBay experiences!  It's not only a great marketplace - it's a fun place to meet people, even if it is vicariously.