If they seem very interested in knives, I will check the knife over and look for what I look for in a knife. I tell them what I like and don't like about their model, I tell them what I avoid, I tell them what I worry about (lock failure). A lot of liner locks I see have a lock that is almost paper thin, doesn't engage well. I see a lot of made in China knives. Outside of Spyderco, I try to avoid getting stuff that is made in China. Sometimes the handle will flex. Sometimes they are heavier than they need to be.
I don't think it has helped anyone, but that's what I do.
One time a friend of mine was carrying a Spyderco Stainless Steel Police. I asked him if I could check it out. I compared it side-by-side to my Endura. It was heavier and had maybe 1/8" more blade. I think I'd prefer carrying a FRN Endura over a SS Police. I don't remember saying anything to him about it outside of them being about the same size and thanking him.