Someone (don't remember who) once posted to the chipboard that they "generally" bid 50% of low TCR on ebay. That way, if they won, they felt they had a good deal....and if the chip condition wasn't quite as good as expected, it was still a fair price. (Mind you, this is not a quote...this is my interpretation of what I remember!! figure that one out!)

It sounded like a pretty good guide to me, so I keep it in mind.

I suspect this is the kind of "rule of thumb" that Dick is looking for....but really, there is no "rule of thumb"...