|Professional Coin Grading Service slab.|
There are fake slabs out there. Mostly Chinese made I have read. Just like with the coins themselves, there is a lot of money to be made by making a fake slab and encasing a coin which is a lower grade than the slab says it is.
It helps to avoid this by using only trusted sellers. At first, that wont be easy for you. After a bit you will make good decisions as your source proves itself. I have been lucky in that I, so far, haven't bought a fake.
For what it is worth, eBay guarantees your purchases. I don't know how that will shake out if you buy a fake and go to them with it. But, it is there in any event. The stats of each seller are online on eBay so you may be relatively certain a seller with a few thousand sales and a 100% rating, or close to that, is probably safe.
There are web sites which go into this in detail if you are interested.
One is here: Fakes
From what I can tell, unless you are stupid enough to buy a coin in a PCGS holder from a Chinese seller, at an obvious low price, you are pretty safe for now. But, stay alert!
I haven't checked into the NGC and other holders, but I'd be surprised if it weren't the same thing.
Now for the good part!
The slabs have evolved through the years and a few have become more valuable. Yes - the actual slab has made a coin more valuable! There are the "rattlers" which didn't hold the coin tightly and rattled. There are the old green holders (OGH) and many other varieties. Some, in and of themselves, can become valuable. A few are quite scarce since only made for a year for example before the next PCGS change.
To see the evolution of the PCGS slabs you can go here: Slabs evolve
I only recently (earlier today) found that page and discovered I may have a few pretty rare ones I bought in the mid and late 80s.