Your using auctions as data points and forget there is one critical point with auctions-people make snap decisions and let emotion take over common sense. You’ll see guns sell at auction they would NEVER bring that on the open market. That is were part of your numbers are skewed.
The problem with trying to publish some sort of “price guide” or “mg blue book” if you will, is that the market is too fluid. What was true a month prior is not working the next. Example- Fleming or Qualified HK sear prices were $40k-$42.5k and all of a sudden the market was flooded with them. Now they are sitting at $45k-$50k and not moving…..why-people saw the market on the upswing and good greedy then flooded the market. “If someone will pay that, then I can get more for mine” once that happens for a few weeks/months, the market becomes stagnant and rather than lowering prices to sell, people sit on them due to pride or whatnot. Dealers will lower prices because they don’t want to be married to stuff, business is about moving inventory, not sitting on it. This is where your data points are off.
Another data point that is off is you aren’t taking into account the auction house commission or the 1099 taxes that the seller will have to pay. You need to take that into account as well which you clearly did not.