The key, of course, is a reputable vendor.
If it's a gun
show of long presence or an obviously reputable larger show (which you can check with venue management), you should start to feel OK.
If it's a first-time or smaller show not previously known to you definitely check it out with venue management, local BBB or via web.
If the particular
vendor sells only knives and has a relatively large display and has been part of the show for a while (which you can check with the show promoter who will likely be on premises) you can feel even better. The show promoter should be happy to brief you on his own experience working with the vendor.
If it's a first-time vendor or someone who strikes you as possibly shady, ask the show promoter how much he checked out the vendor before leasing him space. Ask too if he will stand behind you in trying to track the guy down later should any kind of fraud be discovered; whether he will vouch for the vendor.
Reputable vendors will have on display many of the knives/brands you will be familiar with from these pages alone. They will be knowledgeable and run a clean, well displayed operation. They will spend time with you on questions or requests to examine a few knives.
Get their business card and be sure you get a store receipt from them with business indicia (not some blank, un-numbered form from a bulk "receipt book"), explicitly written and properly filled out, in addition to whatever credit card receipt they may offer should you pay with plastic. If you pay in cash have that written on the store receipt. "Paid cash."
Discuss the warranty with the vendor and get anything in writing that you can, either by way of manufacturer's literature or the vendor guarantee itself.
"90-Day unlimited guarantee" can easily be written by the vendor right on your store receipt.
I also ask whether warranty or exchange will be through the vendor or the manufacturer. If the vendor will involve himself I consider that a plus.
When you're being shown something with which you aren't familiar or appears suspect, someone at the show will have a computer you might be able to use to independently source confirmation of its legitimacy. The vendor himself should be glad to pull up info on his own computer if you appear to be a serious shopper.
If it's someone with a table full of cheap guns, China dolls, carnival slum, promoting bail bonds and displaying knives on a prayer towel then it's caveat emptor. Again, the show promoter is the one to start with for background check.
I've never been really gimped at a gun show. Only near-experience lately was when a vendor told me if the BokerPlus Kalashnikov auto I purchased from him ever broke Boker would fix it for me. They won't. But I didn't really give a damn.
I enjoy browsing the real thing after so many hours of looking at pics online. Armed with some basic knowledge and common sense I think you will find, once you enter the gun show, you will pick out the reputable dealers quickly...and likely have a pretty good time.
Enjoy.