I have budgetary numbers I am comfortable with, typically based on what I may have paid for a product in the past that I want another of. When I see prices beyond what I deem reasonable, I pass, unless I am feely spunky that day and "lowball" someone.
As for many well-known cable brands being in abundance on the used market; are they marketed more than others and simply outnumber competitors and/or are they not satisfying enough to the owners who purchased them (based on the following or curiosity)?
I sold some less expensive Purist cables very quickly as you pointed out and was happy to do so since they did not light my fire in any way. YMMV
I have never dabbled with Cardas, but you are right, they do not seem to be flooding the market. Maybe that's a sign they are keepers more often than not?