I don’t have that link, but this link is pretty much a definitive source.
To get started, you are probably best off buying a “starter set” which comes with a lanyard and a few pins. Then decide WHAT you want to collect. For example, I collect Goofy, Villain and Haunted Mansion pins. Almost anything else I will trade.
Now about buying pins on Ebay: Many of the pins offered are “scrappers” - fakes that are cheap looking and feeling, although they may have been made as run-ons from the original presses in China. Most people - myself included - try to not buy or trade scrappers. If you are paying $0.50 per pin, you can be pretty sure it’s junk - so stay away from those “50 pins for $25” sales. I will usually spend about $2 per pin - which is much cheaper than in the parks. I do buy them in groups, but it’s more like 25 pins for $50. In the past, I’ve used bizzybee1 on Ebay. They seem to have reasonably priced things, and they look and feel authentic
Trade is usually between two people, one of whom may or may not be a CM. If it is a CM, they MUST trade with you, with a few exceptions. I believe those with a green lanyard only trade with children. Also, I think it is a 2 pin max per CM.
If you are trading with another guest, you BOTH have to agree to the trade. If you can’t you both walk away, no hard feelings. Usually I approach a guest (or they approach me) and ask if they would like to trade (if I’ve seen something I would like). If they agree, I tell them what I would like, and they pick something they would like. If both are OK with the trade then it happens. For that reason, I usually take pins I’m not interested in trading off my lanyard.
Other good places to trade are resorts (they usually have pin boards, as do many of the stores), Guest Services in DTD, and even the support staff in the parks, such as the cleaning staff. They usually have something on their belt and are happy to trade. Just stopping to talk to them often brings a smile to their face - I often think they are “invisible” to most people.
I think those are the highlights. It’s a lot of fun, especially for the kids. I’ve bought 100 pins for our next trip, which works out to about 30 per kid. They will even trade between themselves. Again, though, I make sure pins they absolutely MUSt keep are not on their lanyards. Lost pins are a bummer.
Any other questions, just ask.