I think if you live close enough to someone and want to see something before buying and save the shipping charge that it should definitely be allowed.
I have sold/bought a few things on sewitsforsale and was happy with how the transactions went...most buyers want paypal or money orders. At least with paypal, if there would be a problem, a person could file a claim. Always a good idea, especially with a more costly item to purchase insurance incase the item would be lost or damaged in shipping.