I've been though a few speaker cables and several different interconnects from agon. Thats the first place I go without hesitation. I bottom feed and then when I move on I can sell quickly for about what I paid. If you are patient and have cash available, agon can yield fantastic results.
buying used cable is probably safer than buying active components because there is hardly anything that can go wrong with a passive component. The main issue with cables is that they should be in stock condition or the resale value goes very low. There have been some counterfeit cables out of asia. There have been people in the US who buy very long lengths of used cables, chop them up, reterminate and sell the shorter cables as if they are authentic factory terminations. But most of those issues are related to a few high end popular brands. The only thing to look for is that the terminations are factory original terminations. Pictures should reveal that they are in decent shape and some web sites, like cardas, have guides to help identify cables as counterfeit or authentic.
What sort of cables are you looking for? What price rang? what associated gear?
I've had good luck with MIT MH750 and AP silver and oval 9 cables, all less than $300 the pair. If you looking for lower cost, you might consider trying some of the silver clad cables that some people on this site make.