I've never received a defective knife from Kershaw/ZT to date.
I've had a few defective out of the box Spydercos. It's just what happens when you work with human hands I guess. Their Persian, Sage 2, and Leafstorm models all came with gritty action and/or wonky lock-up. I sent it in with the 5 bucks, and got a brand new knife. Yeah if it was a 30 dollar tenacious, trust me, they wouldn't charge you for it even if you broke it yourself. The attitude at Spyderco is "send it in, we'll take care of it".
Kershaw really bends over backwards for their customers and doesn't do anything without customer feedback in the first place. I think their attitude towards the knife game is customer retention, not clever marketing, or "tactical" boasting of any sort. Most people hopping on this ZT/Hinderer collabs have probably been long time Kershaw fans already and stayed onboard due to their generosity. I had a drawer of broken throwaway leeks, I got ALL of them fixed (you really ought not to be cutting cardboard everyday with one of these anyway) for free, no shipping, brand new knives back.
Emerson's customer service is really good too despite making hit or miss knives IMO, it's just that their return shipping costs 15 bucks!
Most companies have their customer service figured out, Kershaw just is one of the top 3 out there. Benchmade is ridiculously easy, I just mailed back a 520 with a at-fault broken blade, brand new blade got put on, sent back, I scribbled BLADE on a receipt and sent it in haha. Wonderfully vague but I think as long as the customer service department of any brand understands that they are the direct lifeline between losing and keeping customers, they'll all do fine!