Just to add on to the PP's information, you can trade with both the blind box (mystery box with 24-doors) and the visible box (three options). The two boxes are often not in the same place in the store, nor are all the visible boxes at registers or at the same register between days. For example, at Star Traders, the blind box was back in the Star Wars room, whereas the visible box was at the entrance.
Also, you cannot offer/trade a vinylmation that is already in the visible box.
For the blind box, I got conflicting information from cast members, so you might want to ask what their policy is before trading. One cast member said you must take the vinylmation they reveal, while two others said you can choose to cancel the trade once you've seen it.
You are only allowed to trade once per day from each box (i.e., only once per day with the Star Traders blind box and once per day from the visible box), but you can trade at multiple stores in the same day (i.e., Star Traders, D-Street, etc.).
A couple of weeks ago, I saw the blind box at Star Traders in DL, the Annimation Palette in DCA, D-Street, and the Tower of Terror gift store in DCA. There are supposed to be many others, but I wasn't looking that hard.
I was told that if the store is selling Vinylmations, then there is a visible trading box somewhere in the store.

Yes - it is really nice if you're looking for a specific one or like to know what you're getting.
I saw on the Disney Parks Blog (when they rolled out trading) that the recommendation was to trade first with the blind box (because you don't know what you're getting), then with the visible box in case you didn't like the blind box vinylmation.
Good luck getting the one you want!![]()
Here is the link to the blog post on the Disney Parks Blog about the vinylmation trading.
http://disneyparks.disney.go.com/blog/2010/05/would-you-like-to-trade/
In the first comment, Steve Miller (the blog post's author) answered a question about frequency and provided the suggestion to do the blind box first.
On a side note, the 3 dolls in the open trading box did not come with the matching doll cards. Not sure about the blind box as we did not try that option.

yeah when ever i traded through the blind box it was always "final sale" but ive only done it like twice and each time i liked what i got, so i dont know if they would have let me have mine back.
but you really have to check to clear boxes to, i have picked up a chaser from them! i dont think the person who traded it realized it was a chaser or something. but i was thrilled!![]()
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Then we did it again one time in Star Traders, and the CM literally took the vinylmation out of dd's hand before she went to the mystery box and when the trade came out as one dd didn't like, the CM would not give back her original one.
What's a chaser?
A chaser is the twelfth vinylmation that are supposed to be a secret. Each series has had twelve dolls, but you are only supposed to know what eleven of them look like (usually shown on the box in a picture). The last one is mystery - though if you look at each series on Disney's Vinylmation website they show what the chaster looks like. You have the same chance of getting a chaser as any of the regular eleven when you buy a new vinylmation still in the box.