A local sale is always easier in my mind as the buyer can actually look the item over and ask direct questions, settle on the product/price and move on.
In a distance sale the buyer may have unrealistically built the item up in their mind's eye and what can ensue is likely to be disappointment. There is great difficulty in trying to describe the item condition while conversing in a linear fashion online/email is difficult at best (FtoF conversations are never that one-dimensional). Even supplementing the description photographically can be a problem as the images can be extremely misleading (the photographer picks what they want the viewer to see, image equipment usually is poor, image resolution limitations on servers, etc...).
I think a big element in the sale is to carefully manage expectations - both seller/buyer. Of course this is easier said than done!
