I LOVE Disney Pins. Every time we go to Disney, I bring all my pins with me! But I can never decide whether to buy pins that I will keep in my collection on eBay or Amazon or to buy ones I do not want to keep and trade with others at Disney! Which is better?
It's always better to get your pins directly from Disney. However I do have some trusted sellers that I will buy pins from between visits. It depends a lot on the pin itself.
I agree with Pixiewings. Buying from Disney lets you know the pin is legit without question if you are looking for something to keep. But, there are good sellers out there that sell legit pins, some as a business and some just narrowing down their collection to downsize or make room for new stuff as interests in characters change. If you are looking to buy on the internet there is a whole thread here about it. Sometimes you just can't get to Disney when a LE pin is released but there are others who can...
You can order pins from Disney directly. I have done that to get pins that are in limited release but not limited edition if I think it will be gone before my next visit. Disney charges a shipping charge based on price so be prepared to pay a lot for that. But, it is great service. You can find the order phone number on the official Disney pin trading site. It is a general customer service number, but sometimes the people who pick up are at Disneyland and sometimes at Disneyworld. They are super friendly and helpful.