Pin trading is fun. You can trade with CMs or even other park goers. As mentioned, the CMs won't refuse any trade, as long as you're giving them a Disney pin - they'll give you whichever one you like of theirs.
I haven't personally had a big problem with fakes, but I also don't care that much - my kids enjoy it, and they just trade whatever they see and like. Its fun to interact, seek out traders, get new ones, see what others have, etc. Plus, wearing their lanyards full of pins is just part of the wardrobe for our Disney trips!
This upcoming trip, they'll be popular little girls because we haven't been to WDW since they started collecting. Many of their pins are DLR-oriented, so the WDW crowd will likely be into them.
Between penny pressing machines, autographs and pins, there's so many fun little side things for kids to do - they love it, and I love watching them!