There's two kind weapon you can find in warehouse and reno:
rare - like gauss pistol/rifle, gatling, vindicator.
unique but normal - like sniper, pancor, flamethrower. They have nice stats (always -ap), but they're worthless. Well, maybe not worthless but 10-20k max, when rare weapons start from 200k, because rare weapons isn't craftable.
That's why nobody gives you 300k for unique sniper. Anyone with 100k can buy mine and craft like ~1k sniper rifle and probably ~10 of them will be unique.