If you go onto msn.com and then do a search through their search engine for "Garmin Zumo 550", there will be one at the top shaded in blue with a link to Ebay. It will show that it is a "BING Cashback" item with 8% cashback offered. When you click on that link, it will take you to Ebay and you will see that item, again marked with the cashback markings next to it. You have to purchase on the "Buy it Now" and pay through Paypal to get your 8% cash back.
You have to sign up for the BING (Microsoft) cashback also. I just did a search on BING cashback and clicked on the one of the links to setup a username and password, etc. You obviously also need a paypal and Ebay username and password. When you buy the item, it will tell you right away that it qualifies for the 8% cashback and after the paypal screens, another screen comes up to enter your login info for the BING cashback.
This is not something that is set up for every purchase. It's only on specific items from specific vendors, so you have to choose the one that is labeled that way from your search and buy that particular item. It just happens that the Zumo 550 was one of those items, so I went ahead and signed up. The seller on it was something like 7 Fold GPS and they have a good rating. The cashback does not come from the seller, but rather from Microsoft. It will be deposited back into your Paypal account, but it may take up to 60 days, since they have to wait to make sure you didn't return the item to the seller.
If you try it, and end up with questions along the way, post your questions or PM me or whatever. I'll try to help, but it was pretty straightforward once you know you have accounts set up with BING, Paypal, and Ebay. Happy shopping.