That's not how it works?

If a hat gets sold for less, the "dumped" sale (for lack of a better term) is not magically invalid as well. 660 reselling for 440 doesn't make 440 invalid, it only makes 660 invalid. 440 can still be used perfectly fine. If things worked like that, nothing would get priced and every single suggestion would either be a price raise, or a revert because the previous suggestion is now void.

The logic behind excluding the higher sales, is generally that the buyer of the previous sale didn't value it as much as what they bought it for. There's exceptions, of course. But generally speaking, if someone were to buy a hat for say, 150 Keys pure, then they resell it for 120 Keys pure, then it was clear that they weren't confident that their hat was actually worth the 150 Keys, so the sale gets thrown out. Whether the motive for selling for less is quickselling, cashing out, or whatever else doesn't really matter, as we can't get into the minds of traders who toss out money spent for whatever reason. We can only work with the objective sales data presented to us.