Also alot of the numbers you see are "listed" numbers. If you want to see what things are actually selling for, you can look on gunbroker at closed auctions and see what they actually closed at.
I was wondering about the same thing the other day.
I guess people just throw it out there and see if someone grabs it. You know like fishing...for idiots instead of fish. LOL
Check out this $6,000 Bushmaster: https://www.gunbroker.com/item/893185815