This website tracks the market value of used camera gear ...

MICHAEL ZHANG, PETAPIXEL:

Want to quickly find out the current market value of a used camera or lens? Bokeh Market is a new website that can tell you the real-time value of used equipment. It’s like the Kelley Blue Book of camera gear.

The front page features a search bar. Type in whatever piece of equipment you’d like to look up to bring up its product page. The product page features the products specs, a daily price chart that spans about a year, average prices for individual sellers and trusted sellers, and ongoing listings for the product through various marketplaces (e.g. eBay, Adorama, Amazon, KEH, Fred Miranda).

Check it out, from here.