Here is a link to some of the basic guidelines from Disney:
http://www.disneyparksmerchandise.com/parksauthentic/disney-pin-trading-guidelines-for-guests/
Some other basic information about pin trading...
I would also recommend looking into buying some starter sets pins or lanyard pin sets. If you live near a
Disney Store Outlet, I would check those also for inexpensive pins. Finally, the DisneyStore.com sometimes have pins on the clearance sale section of the site.
If you buy pins on eBay, be aware that many of the pin lots (e.g., bulk buying) tend to include scrapper pins. These look like official Disney pins, but they're technically pins that are not legitimate. They can be anything from over-runs to pins that failed quality control tests to outright knock offs (think Ariel with brown hair, Belle's yellow ballgown is green, etc.). If the pins tend to less than $1.50 each, that's generally a sign it'll be scrappers. Now having said all of that, if you daughter trades with CM's there is a 99.9% chance likelihood that at some point she'll get a scrapper. They're pretty prevalent on the CM lanyards. For some, that's a deal breaker, for others it's just something to be aware of, but it's not a big deal. It's up to you to decide how much getting scrappers would bother you.
In terms of trading with CMs, they will always accept the trade as long as a few basic requirements are met. The pin must have the Disney copyright logo on the back, it must be in "good" condition, it cannot be personalized, and they cannot already have the same one on their lanyard. Other than that, they'll accept it. Trading with CMs is "safe" because you don't risk rejection or scams.
Now, there are also "professional" traders. These are folks that are trying to make money while trading. I'm sure there are some nice/honest ones, but most that I've run across seem to be trying to take advantage of other (less expert) guests. If they ask you to buy them a pin in exchange for one of theirs or make anything other than a one-for-one trade, I'd walk away.
As for the lanyard, that depends on your daughter. I'd consider having a little baggie or something to put the pins that she really wants to keep into. The lanyard are great for displaying pins, but pins can fall off and be lost. Also, the lanyards can get heavy over time and get snagged on things.
In addition to the CMs that are wearing lanyards (some around the neck and some at their waist), there are also pin books and boards scattered throughout the resorts and parks. You never know where one might be, so keep your eyes open and be sure to ask! A lot of the Guest Service locations in the park have one, as due some of the resort check-in desks.
Pin trading is a lot of fun, but it can be very addictive! Just keep that in mind and be aware that you might be starting something from which there is no return!
