I prefer it when the price is left. It takes no more than changing colors to let everyone know very vividly that the knife is SOLD. I like to follow general pricing trends, and that can't be done when the prices are removed. What did the knife actually sell for? Can't be sure, but I can at least see what it was advertised for, and with enough sales threads, something can be gleaned.
I also don't think one person's 'fire sale' has anything to do with what a maker can charge for their knives. No one is gonna go to a car lot and demand a discount because someone sold a used car of the same make for well under blue book because they were in a tight spot. If everyone left their prices up, then it would be so very easy to see where the outliers are. A single private sale on BF doesn't mean anything, and if a lot of sales are going on below what the maker wants to charge, then that is the market telling him something.
It also doesn't mean anything if you made a profit on the knives. Plenty of production knives increase in price, at least in the short term. There are people selling discontinued Benchmades and Spydercos for twice the original/average net price, and they can't hide that fact because a ton of sites still list the knives with prices, even though they are out of stock. New Graham does it on purpose, for the exact reason of providing visitors a historical reference of their pricing.