I usually will shop on the marketplace, and then look in world if its something I actually want to buy.
Usually on the marketplace the items presented have been so overly photoshopped or edited on a pose stand so much to fit the model well... that they're nothing like the out of the box item. I prefer to see the item in world if I'm going to be spending a good amount of money on clothing. No photoshopping, show me how the item moves on an avatar... show me you actually can work with prims well rather then looprez. Then I'll be a devoted fan and probably buy in store and in marketplace.
With furniture, if the item is highly photoshopped or edited or has items in the photo that are not the item offered, I tend to avoid that item. Yes I know that photoshopping happens, and editing happens, and props look nice.. but I'm buying an item, not your photoshop skills in making pretty light effects, not your ability to place the text for the item RIGHT over the major flaw in the item's design. I'm buying the item. Also with furniture I'd like to see that you're not using freebie animations with the furniture. Either custom made poses/animations or well done full perms ones is good. But I'm not spending 5000L on a couch that has nothing but a free MLP drive in it and freebie animations. Great, you edited a notecard.... that's not worth 5k in my book. So if there's a store available for me to test the animations and to see the primwork, that will make me part with my lindens a LOT more than a well done ad on the marketplace.
Be very polite. -Flagg RIP 2009