I've had more than a dozen dealings with AQ service. They're great. More than 90% of the time they're very prompt to issue an RMA. I've had one request slip through - just try again. I just got issued another RMA this week. I've never had any of the used AQ cables I've sent to them flagged as counterfeit - so far (knock on wood).
Discerning counterfeits these days is a real challenge. Search through AliExpress and see how closely some counterfeits now emulate the current Mythical Series speaker cables and PCs

Basically, superficial analysis of pics can only go so far. You have to trust your sellers, AND those sellers need to have tracked ownership all the way back to a legit source. There used to be a few telltale signs of AQ counterfeits:
* Interconnect models featuring air tubes should have a wire "chatter" sound when tapped
* Open the interconnect or speaker connectors and visibly confirm the wire is solid core of the right metals. Take care that silver colored metal is actually silver, not steel or aluminum - because that's a thing, too. Some of the more sophisticated Sky counterfeits would use Columbia (copper) innards with the exact Sky outer braid (these would also pass the rattle test!).
* The velcro battery pack straps with white "audioquest" text on them is a dead giveaway of a counterfeit. These were also thicker and fuzzier than the actual velcro AQ used. AQ never used white font on their straps, IIRC.
* Many counterfeits of Tree-series speaker cables had a very lumpy / kinked appearance to their outer cover & braid (looks bad); real tree series is very smooth and kinkless.
However, many of these "tricks" have broken down. Also note that a braid cover going "hairy", even on new-ish cables, is NOT necessarily a sign of counterfeit. Their current braids for Hurricane / Thunderbird / Firebird are very susceptible to this. I wish they'd address it as it detracts from the otherwise high quality feel of the product.