What's the best website for finding value of used gear?

[CMJeepster]

I've got a relative that's potentially looking to clear our her deceased husband's large collection of gear (mostly freshwater). I haven't laid eyes on it yet, but I've got his inventory notebook in my possession and am planning to make a spreadsheet for her to show inventory and approximate value. Depending on the value and condition, I might buy the lot for use or resale. I've never done anything like this before, so I could use some help getting pointed in the right direction. Thanks!