My best advice when you are buying off ebay and looking to avoid fakes (which you should be doing) is to try and find someone selling off pieces of a collection. The best way to tell is by looking at their ebay history and looking at what other things they have for sale. I would also look for lots that don't heavily feature hidden mickey pins, since the majority of those are fakes. Sealed booster packs are generally a good bet. Lots that say things like 100% tradeable and don't show you which individual pins you are specifically going to get, or pins in small plastic baggies- most likely fakes.
If a seller sells thousands of pins a week, then they are most likely fakes. If you find a seller that is only selling a few lots, and then sells a variety of other things, than you are most likely not dealing with a scrapper wholesaler.
You really have to look and wait for the right lot, there are deals to be had for real pins, but they take some time and persistence to find.
That's not saying that someone's collection couldn't contain fakes, I own probably about 1000 pins, and I'm sure there are some fakes that have slipped by me, but a collector is less likely to outright sell fakes from china.