If you're looking to trade items into a shop, KEH appears to be the highest paying game in town from what I've seen. They offer more than B&H when I did side by side comparisons.

That said if you're trying to sell something of any value you're best off with a person to person sale.

Items that aren't worth that much or are hard to sell are different. KEH was close enough on my 18-135 and 28 f/1.8 to make it worthwhile to trade them in. I'll eventually sell other stuff (Zeiss 50 and 135L likely for sure and possibly 70-200 f/4L, and 1.4 II extender) and think I'll likely use the Fred Miranda forum for those.

Dave