Actually, rare items have been priceable with one sale for as long as I can remember. The fact that they are is greatly favored among the community as it enables items that rarely have more than one sale in a 3 month timeframe to get a price tag too, instead of them sitting unpriced in backpacks. Collectors and people that play the game in particular even, because they're usually the ones that make purchases on this kind of unique items.

Of course, we generally prefer to have more than one sale to ensure we're not pricing items off of outlier purchases. This sometimes leads to frustration of people that feel they made a good deal or paid far less than something can realisticly go for, as this also means that some items could be priced below their maximum potential, but then again - that works both ways.

As an avid weapon trader/collector, I wouldn't even say this is necessarily low. Weapons tend to be more versatile based on personal opinions. Rare weapons stand out; the weapon market has been overflown and the lowtier unusual weapon market collapsed after the release of warpaints, which in a sense struck all weapons. This makes tier comparison on weapons that have remained rare harder, but seeing a non-strange fac new assassin grade shotgun at 280 doesn't strike me as odd.

Don't see this as me telling you can't possibly sell your weapon for more, or that you are not allowed to value it higher. As said, if you sell it higher, the price can be updated again - this way, the system allows itself to fix values that are high/low, once the market proves this to be the case.