I won't pay "New" prices for used off-the-shelf items that I can order in-stock from dealers, but I have bought and sold a few custom rifles at "Near New" prices. The three main factors are:
(1) The Builder: His quality of work, attention to detail, how he backs up his work, and to some degree, his backlog.
(2) Component Wait Time: If I ordered the components, how long is the wait for the action, barrel, stock, etc?
(3) The Seller: How well does he take care of his equipment? How accurate is his round count on barrels and action? eg less than 300 round (guesstimate) or exactly 731 rounds fired (barrel log). Is he a man of his word?
When I see a rifle of interest for sale, I consider the following:
How badly do I need it? When do I need it? What are the total cost of components, labor, and shipping to build today? (One thing I notice---when people are doing the component and labor list, they usually forget all the shipping costs involved. I've yet to receive free shipping, insurance, rifle cases, or FFL fees on my builds.)
For example, I ordered a BAT MB receiver on Feb 28 and it will arrive at my FFL on Monday, Oct 8. I will then ship it and the other components to Jon Beanland who currently is quoting a 4 to 5 month backlog. That is a total of 11-12 months for a build that was only short one item: the receiver. I already had the McMillan A-5 stock, the BAT 308 bolt, a Krieger barrel blank, the Williams ADL T/G, the Jewell trigger, the BAT 20 MOA Base, the Badger Ordnance rings, and NF NXS scope.
This is not my only rifle so I am willing to wait.
Some day, this rifle will be for sale. What will it bring on the open market?
For someone with a bad case of wants, needs, or impatience, he may just pay my "Near New" price on a premium built, well cared-for, used rifle. If not, then the price would be adjusted until it meets the price that someone is willing to pay or that I decide to keep it.
It is pretty much supply and demand. If I want it badly enough, I will pay top dollar. If not, I will watch for price reductions and risk losing it, or I will scroll on down the page and forget it.
Few need more than one rifle but some "want" several. I am one of the latter.