It turned into an auction when he said start at $50 and see where it goes. Good luck to the bidders!
To me it defeats the purpose of the classifieds on an enthusiast board, a pretty quick search on eBay can give you a good idea what to ask, and then saving about 12% in auction fees by selling here should soften the price a little. 90% of the forums I'm on have rules to prevent unsanctioned auctions as they can get messy quick and there is no benefit to the buyer.
But since they don't have that rule here he's doing nothing wrong, bid away people! When does the auction end? Did you bid? What's the current high bid?