Buyer beware on those purchasing proof sets from 1955-1964 as unopened.  I know for a fact that many dealers (including one that I do a lot of business with), PRINT THEIR OWN ENVELOPES or buy pre-printed envelopes from other sources.  These envelopes are printed to the same specifications as the original US mint envelopes.  You know that these proof sets have probably already been searched for valuable cameo coins as well as double dies, etc. 

On a different note, it is truly sad that eBay has become the dumping ground for problem coins, overgraded, fuzzy or no picture auctions, estate sales with the excuse of no returns, etc.  If sellers cannot present a large, clear/detailed picture of the item(s) you are looking at and does not stand behind their sale by offering a refund option, stay away.  You will most likely get burned.

I could write a manual on my experiences with unscrupulous sellers, scammers, fraudsters, etc.  I do my part all the time to expose these people to the "ebay police" and the real police if warranted (I've already turned over several for prosecution).  After all, it's these people that hurt my legitimate business in the long run by scaring people away.