Experience with Adio Equipment Trade-Up Promotions

Anyone have experience with vendor "trade-up" promotions where they buy your used equipment and apply your trade-in as store credit towards a more expensive piece of equipment they are selling?  Are you much better off selling your used equipment elsewhere (e.g. Audiogon) even if you intend to buy equipment from the vendor (e.g. MusicDirect)?

I'm curious on your experiences.  Thanks in advance!
I'd make an analogy to trading in your used car for a new one.  You can (usually) get more if you sell it yourself, but it can also be a hassle.  

Suggest that you get the store's offer and compare it to prices here, EBay, etc.  If it seems fair, trade it in.
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Any trade in will be less than what the item could sell for on an open market. Obviously, it takes more time, effort, and likely some expense to get that best price when selling. Only you can decide if the extra is worth it.

Thanks for all the input and perspective guys. Clearly it wont hurt to see what they offer for my used trade-in and I can assess and go from there.  I do highly value avoiding the hassle of listing, shipping, and dealing with an unknown 3rd party so I'm certainly willing to price that aspect in.