In my case, the key to purchasing RAW Errors on
ebay is self educating yourself on knowing what's real, what's fake, and most of all the Rarity of the item & maximum amount of the Bid to place and receiving it at a fraction of the Bid..
When the Mint cracked down on the number of errors entering circulation in 2002, multi-struck coins, other than
State Quarters, were almost impossible to find..
When the 2003-d quadstruck
LMC was listed in 2004, I knew it would be Unique as all 4 strikes had been Die-Struck with no 2nd Planchet involved as found in most multi-struck errors..
On my Currency purchases, all 3 Natick Test Paper overprint errors & both Web-Press overprint errors had been listed as regular errors omitting the fact they are classified as Experimental Notes.. It was after I purchased these that I decided to post my personal research data into a Public Census with serial number charts showing the Rarity here on CCF..