I guess I have a different viewpoint on the subject. I've been buying and selling amateur equipment since 1959 for personal use only - not trying to profit from resales. In the early 60s, the only way to reach a wide audience when selling something was to advertise in the classifieds in QST or CQ magazine. Otherwise, your potential buyers were local radio club members. Technology was advancing rapidly at that time and everyone I knew wanted the latest and greatest gear and there was very little demand for out of date stuff. So, you would set a price at which you could be pretty sure of attracting a buyer and send off your add to a magazine. Some months later, the ad would appear and if you set your price right you might get a letter or two from prospective buyers. In our area, no one attempted to make a business out of profiting from used gear and most guys would sell to newcomers at low prices just to help them get started.
About the same time, a publication known as the "Yellow Sheets" came along - published a couple of times a month, 5-6 double-sided pages printed on yellow paper. Then we could run an ad that would be seen in just a couple of weeks by hundreds of subscribers across the USA. Not as wide a distribution as the magazines, but the readers were active traders and so your ad reached a larger group of potential buyers. Even with that, prices remained fairly stable.
Thirty years later, the Internet came along with multiple websites containing classified buy/sell ads and now you had a world-wide pool of potential buyers. Without fail, somewhere in that pool of buyers was a guy who wanted what you were selling and was ready and able to pay any amount to get it.
That was fueled by the emergence of eBay, where such buyers would compete against one another, driving prices insanely high. Some of you may remember back maybe 20 years ago when Joe Walsh bought a Hallicrafters SX-88 on eBay for an amount north of $4,200! The SX-88, while rare, was a mediocre receiver with horrible intermod performance and it didn't come close to a receiver like the Collins 75A-4. But, Joe's bid set the price level of the SX-88 for the rest of time, and they still command absurd prices.
When you get ready to sell a piece of gear today, the first thing you do is get on the Web and check to see what price everyone else is selling the same thing for. That tends to stabilize the price of an item years past the point where it would have been reduced based on its performance vs. other gear. And, lastly, there's the Collector problem. When I was getting started, there were few if any collectors of amateur radio equipment. Today, there are collectors of virtually EVERY brand of radio gear. They will pay any amount to improve the "quality" of their collection, driving up the prices of the better quality gear. My first experience with one of those fellows was the European who paid me $225 dollars for a set of unused IC-781 handles (!) still in their original wrapper. I had paid $19.95 for them new.
To sum up, somewhere in the world there's a guy with a burning desire to own what you're selling and he is willing to pay anything you ask for it. Today, that guy will likely see your ad on the Web, whereas many years ago you and he would never meet.
73, K8AC