I've been dealing with KEH since the late 70s, when they were just starting out. In fact, I used to see King Grant, the founder, manning his booth at photo trade shows where I also was buying and selling in those days. I've always been pleased with the stuff I've bought from them. The best, probably, was a 40mm Zeiss T* lens that I bought for my Hasselblad in the late 90s. They listed it as BGN, but it was thoroughly E+ and I later sold it for more than I paid for it.
On the other hand, I don't sell to them. I can always get more for my equipment by selling on fora such as the one here, POTN, and photo.net.