Whenever this sort of topic comes up, I always feel the need to voice my opinion:
I have flipped several keyboards on here. A Filco TKL with browns, a Model M SSK, and I think there was at least one more, though I can't remember off the top of my head. In the interest of full disclosure, I paid $50 for the Filco, and $67 for the SSK. I sold the Filco for ~$95, and the SSK for ~$150. In retrospect, would I do it again? It depends. I didn't have much money a year ago when I joined GH, and saw an opportunity to sell some stuff without eBay fees. So when I saw these keyboards pop up, I bought them, almost entirely with the intent of selling them (I wanted to try browns, but expected not to like them.) I could use the extra couple bucks, and at the time, I didn't see much of a problem with it- to a degree, I still don't. If you need money, I'm not going to crucify any flippers. I've done it before, and it's entirely possible that as I enter a college I am not completely sure I can afford, I may do it again. That being said, nowadays I have given some stuff away and been given some stuff for free, seen the community come together to raise money for a member's pet's operation, and sort enormous quantities of stuff for fundraising auctions. That has helped me realize that many people here are good enough people that I will do them a favor or cut them a deal. As for auctions, I personally am in favor of complete transparency- an unjust individual could artificially increase the price of a PM auction, which would be bad. I also think it is unwise to not consider the depreciation of any investment upon purchase, be it a keyboard, real estate, firearm, or who knows what. Anywho, just my two cents.