I generally won't ship if the item is too big/heavy for my wife to pick up. I'm not able to do it myself. Unlike the other hobbies/forums I'm involved in, this particular hobby is one that could require the use of a forklift to ship parts.
A lot of people want a shipping quote first, which means I'd have to palletize and weigh it... then get offended and try to tell me that they can get it cheaper, or they want a "discount" to offset the cost (making the part nearly free!)... and end up not buying anyway. It's simply not worth the headache on a low-buck part, but if I'm trying to sell a $1500 axle or $1000 set of wheels, it's worth some effort. I guess I also just have a low tolerance for flakes, and face to face cuts down on "those guys" considerably.
I've got a pair of fiberglass fenders for sale right now that I "will not ship" as the first time I got a quote was over $125 to ship just a few counties away and the "buyer" flipped out about it! I'd also be concerned about them getting damaged in shipping, and the headaches that would be sure to follow. The vast majority of this forum, and several others that I frequent, have been outstanding, but window shoppers are everywhere. Even on this forum, I've had people "commit" to buy, and then no show/ no pay/ no response after I've held items for them, or packaged them up to ship.
I've had no problem with giving stuff away on this forum though, people have managed to drive from all over the place to my location to pick up seats, springs, consoles, axles, magic beans, racks, etc. and I've even picked up the tab on shipping a few free items. It all balances out I guess. Besides, isn't this forum for people who like to go exploring/on adventures in their SMB's/vans? Maybe we should require that buyers must make the trip to pick up?