I can see how it can be hard to sell equipment though especially when one can drill a couple of holes and get some fittings and they are off to the races.
It depends on what one wants. My first all-grain brewhouse in 1993 was DIY because that was the only way one was going to brew all-grain beer. I also kept a yeast bank on agar slants for a very long time. There is no longer a need to DIY a brewhouse any more than there is a need to keep one's own yeast bank.
The stuff I sold was all top-shelf gear. There are people aspire to have top-shelf gear, but do not want to pay the cost of new. That is where used comes into the equation. The lowest end piece of gear I sold was my 10-gallon industrial Igloo cooler-based mash/lauter, but even that cost me the better part $150.00 to build. Heck, the cooler alone cost $75. The false bottom cost $40.00. I used a custom-machined bulkhead and other quality fittings (I have paid my dues dealing with off-the-shelf standard NPT parts for bulkheads). It all adds up. However, the mash-tun was optimized for continuous sparging. False bottom and tun design are critical when continuous sparging.
One can use any 10-gallon stock pot to boil wort, but one cannot use any 10-gallon stock pot with a portable 3500W induction range. The stock pot has to be induction ready and better quality than the Bayou Classic garbage if one wants to be efficient. I have not brewed with propane in a long time. Same thing can be said about a mash/lauter tun. If one wants cheap, nothing is cheaper than a Zapap lauter tun. As I mentioned earlier, what one desires dictates cost.