I've always seen a 4 tiered system for buying a used pin, each with their own audience and price point:
1) untested, no warranty, as-is, and "don't call me" - by far the cheapest and some would say most "fun" way. I got my Super Soccer this way out of the back of a van at a show. It "mostly worked". And the seller was right.
2) tested, no warranty, as-is, and "don't call me" - a more typical purchase. Try the pin at a show or the seller's house, but you get what you get and you don't get upset. Obviously, it's a little less risky than #1 and the price is slightly higher because of it. This is how I got my Home Run and Cleopatra.
3) retail setting, short warranty, "call me, but I'm not your best friend" - for those who know a little less than the average owner, or are looking for a particular machine and aren't willing to troll shows, craigslist, or pinside for months / years looking for it. You are paying for a service. I'd be willing to purchase a pin this way, if it was the right one at a semi-reasonable price.
4) high end retail, long warranty, "I'll come to your house, set it up, and pretend to be your friend" - for those who know very little about pins and have lots of disposable income; showcase man caves where having a restored coke machine is the norm. I have a hard time seeing myself getting a pin this way, but I know someone with more money than a reasonable person should have that has bought pins this way. They were happy with their purchase, so who I am I to criticize?