I made one on-line order so far with KEH (RB67 6x4,5 back wanted for an RB67 plain) . Then I sent them a bunch of worried emails about only shippign if it would work with the 'plain' RB.
I think it was a bargain or UG and only $34.
While I didn't get a response, it arrived quickly, was in fine condition - I can't even recall seeing anything wrong with it.
It was described as not having a viewfinder mask - I don't even know what that is, so I didn't miss it.
It is apparently for the RB67 Pro or Pro S as it has the dark slide interlock (I wasn't expecting that feature).
So I was very happy, usually bargain hunting, and have had alot of flaky descriptions on eBay.
Admittedly, I didn't gamble much, but I got something much better than I expected.