A couple of points to consider, first, the difference between what something might sell for at auction (Gunbroker) and what it is actually "worth".
OF course, there are those who will say that "if it sold for X, then its worth X" and while true, it can be true that its only worth that much to that particular buyer at that moment in time.
People will often pay a premium to get what they want, "NOW", and especially if it is something that isn't a common item, easily and often found for sale.
Back in the mid 70s, a friend of mine paid $450 for a (lightly used) S&W M29 .44 Mag. At the time, MSRP on a new one was $283.50. Why did he pay so much?? because, at that time S&W was running about 2 years backorder on that model, and the guy who had that gun was asking $450 to sell it to you, TODAY.
IN the pre internet days, LOCAL supply and demand played a bigger part in the value of a gun than today. You got a better price selling a "bear stopper" in rural areas that have bears than you would selling the same gun in a metro area, and the reverse was generally true of pocket pistols.
Advertising on the Internet today gives you the whole country (possibly the whole world) as potential buyers, instead of just people reading the local want ads or seeing the gun in a local gunshop. This has gone a long way to leveling out regional price differences, but supply and demand, and getting it now vs. having to wait still plays a role.
Auctions (especially online) can result in you getting an item, at a savings over its usual price, or can result in you getting well over the usual price for an item if there is a bidding war.
I recently sold some virgin brass in .375H&H on Gunbroker. Initial bid was set actually slightly below "market" value. As time began getting short, bidding went up. Couple days before the end, bids were up to double initial, and in the last few hours, tripled. Because someone one wanted it, "now".
When it comes to pricing guns for sale, what is your priority? Getting some portion of the gun's value quicky? or getting as much of the guns value as possible? Because that will generally take much longer.
Good Luck!