The 50mm f/1.8 II is such a low cost lens I fail to see why anyone would buy a used one and give up on a warranty.
I'm also a bit against selling anything to a friend - lend it or give it away, but not sell, especially for THIS lens. finanially there is so little to gain, you can't easily ask a friend to pay a fair price, and you're not even sure you want to part with the lens!
I'd suggest lend it to your friend so thay can see if they like it, if they do, they can shell out the 80 bucks for their own copy, and if they don't, you've done them a favour. either way you still have your lens, and your friend!