There's a lot one needs to be aware of when buying certified coins regardless of where one is doing the buying:
1) fake coins in fake slabs;
2) genuine coins in fake slabs;
3) genuine coins in fake slabs with exaggerated grading or irregularities that make them un-slab-able;
4) genuine coins in genuine slabs that are graded improperly or not properly identified;
5) fake coins in genuine slabs (recycled body parts from crack-outs);
6) genuine coins in genuine slabs that are doctored;
7) genuine coins in genuine slabs (switched higher grade authentic with a lower grade coin or problem coin);
😎 genuine coins in genuine slabs with changed inserts;
9) fake coins in genuine slabs (grading service mistake).
The grading services were established particularly for the coin buying public to reduce the risk of purchasing over-graded or problem coins. They were not established to authenticate -- with the exception of rare US gold and the occasional key date coins. By default, and due to changing market conditions, they now first authenticate the submission and secondarily determine if the coin is gradable and if so, do so.
In effect though, the certification services have made coin buying a highly risky endeavor. Only for those with the resources and skills who to know how to authenticate and know grading as well as know something about numismatic forensics and counterfeit detection when encountering a certified coin. For all others it is a crapshoot.
Before one decides to buy the coin one must 'buy' the seller/dealer. This is where anonymous sellers and those especially located outside of the US have taken eBay by storm with their nefarious goods.
My recommendation today is to not purchase certified coins on eBay due to the unacceptable level of risk. Sure, there are SNAD procedures and other forms of recourse, but why place one's hard earned funds in the hands of another entity not party to the transaction and one who may have an agenda of their own that is not in your best interest? Instead, one must perform due diligence on both the certified coin and the seller beforehand. Only purchase certified coins, in person, from a known seller/dealer, with terms of sale agreed by both parties in writing.
