There are two challenges with buying counterfeit knives (and perhaps anything).
If the knockoff is being sold as the original manufactured knife you shouldn't expect to get the same quality or materials as the original and there's no assurance of it. Knockoffs come in all sorts of levels of quality these days. Since marketing can claim anything, you have to expend effort to try to find the knockoffs that are of better quality. Can you even trust the results after extensive review? Hard to tell since knockoff manufacturers knock off each other and rip off the same marketing. That means that price point above "so cheap it is obvious" it has to be a fake (like our $22 Benchmade that started the thread) may be better or just more of a ripoff. With knives you can at least check a couple of reviewers who specialize in Chinese made knives, both knockoffs and "nearly likes" that have inside information and extensive experience. That can give you some guidance on value. But, you face the problem that knockoff manufacturers are knocked off so the good review on the Sanremo knockoff (for those that don't know Sanremo was and perhaps still is a notorious copier of Sebenza's style) may not apply to the Ti or steel frame and certainly won't to the copy of the Sanremo being knocked off by a lower tier fake maker. It is a constantly shifting area of interest. What's the consequence of buying fake you didn't know was a fake? Performance probably won't be as good or may be horrible. Your "too good to be true" priced knife may come with a properly heat treaded D2 blade that cuts pretty well or you may get one that they skipped the heat treat to save some money or they may just put a 420J steel in place to keep it from rusting and some sort of edge on it assuming you won't fuss if the price is low. You can't tell because they are interested making you think you got the real deal at an unbelievable price and nothing more. So, is it a properly heat treated D2 blade or some mystery metal? Dunno. Mechanisms are certainly another place you can be cheated on. Is it a bearing system as advertised or a nylon washer? Will you know and will you go to the trouble to demand your money back if you can tell? You were sold a Benchmade/Spyderco/Sebenza and your expectation is that you can trust the quality in materials and construction so the knockoff companies gamble they won't have to pay anything back because people want to believe they have the authentic and those that find out they were cheated won't put any effort into trying to get their money back if they're not out too much. Manufacturers care because of the damage to their reputation and just about every manufacturer has information on counterfeits because it hurts their reputation and business. I have handled Cold Steel san mai knives that had to be coming off the loading dock from the same factory as those going to CS for sale. The quality was indistinguishable, but the price was half of the CS discount prices. The boxes were cleverly done as old style boxes so the knives could be sold as New Old Stock. I have also handled many more that were obvious fakes that ranged from those that would pass a cursory examination to those that you could spot as fakes from feet away. I've done this with Microtechs and Hinderers and other high end production knives. (A dealer friend handed an MT OTF to me and without even looking I handed it back telling him is was a knockoff just because of the feel). The higher the price of a production knife (Sebenza, Microtech, etc) the greater the likelihood knockoffs can be of surprising superficial quality. It can be tough to know depending on your experience. I've done the research and and still am constantly behind the counterfeiters.
There are knockoffs or "nearly likes" being sold openly as a knockoff and their marketing is up front about it. You see this on Dhgate and other Chinese marketplaces and sometimes even on ebay. You may have to learn to decipher the phrasing or they may be very clear about it. That makes life a little easier because your fake MT is marketed as a knockoff. They will tell you that the blades are D2 or VG10 or ATS34 and they won't claim the more exotic steels used by the authentic manufacturers. Is that better for the buyer? Yes, but... But there's a wide quality range in these knives and you have to know the reviewers to trust or you have to research the manufacturers to know the quality range. They're still stealing the intellectual property of American and European and Russian companies, but they're "honest" about it. You won't expect it to look or perform exactly like the authentic knife. You won't try to send it to MT/BM/etc for service knowing it is a fake. So your expectations are lower and the price you pay will be closer with those expectations. Still not good, but not like being lied to.
What stops resellers from buying fakes and selling them as authentic? Nothing. Some resellers started out selling fakes as authentic and without any concern for the quality. Some progressed from there to being interested in quality fakes (real D2 with real heat treat) as the authentic. Some of those I know progressed from selling enough of those to get deals from the Chinese to make something that they sell as their own brand (lots of Microtech knockoff designs out there). They have them coated and branded not as MTs, but at "Bear Cat" or "Lightning" or something else. The blades are good D2 with heat treat and they put American springs in them and have their own packaging and they assemble them themselves from parts shipped from China. They don't look exactly like MTs, they're not marked like MTs, they're not packaged as MTs, they're not marketed as MTs, but they're riding the coattails of MT. Is that far enough away from counterfeiting? For just about most consumers it is.
The examples of Rolex watches and sunglasses was brought up. I'm not a watch collector, but I like watches and I have a couple of expensive watches in the Rolex range. I grew interested in the range of watches being sold and that included the counterfeits since I always wanted an Omega "Moon Watch" being a space geek. That interest led me to forums and websites just for "clones". These folks review the various counterfeit Omega and Rolex and ... (and even Seikos) watches. The sites are easy to find just with a search. They discuss and debate the quality of the counterfeits and how close they are to the authentic watches and it is fascinating to read and watch their assessments. They even discuss the counterfeits where crooks take non operating Rolexes and Omegas, drop modern automatic or even quartz movements in them, and then try to cheat people into paying the authentic price (you can tell the electric from the automatic movements once you learn how the second hands move in each). So as we know the range of "clone" to "counterfeit" is seen in expensive watch copies and the folks interested discuss them and rate them and even buy them (like the Chinese knife reviewers), but they don't pretend they're the same and they know the embarrassment for being found out if they pose as wearing one claiming it as authentic and they don't advocate trying to get them serviced as authentic since they'll be outed as fake. They also discuss the watches that are "honoring" the past iconic watches by reflecting the look without branding. The most common being "pepsi" automatic dive watches or early iconic watches like Hamilton's own Ventura they updated themselves and reissued. At a glance a Victorinox stainless dive watch might be mistaken for a Rolex dive watch by someone that doesn't know either, but not by a Rolex enthusiast. No shame in it since Victorinox doesn't hide who they are.
We all know there are fakes sold as authentic, whether watch, sunglasses, knives, or anything else of value. If they manufacturer and seller is open about the fact they are "inspired by, but are clearly branded as something else that's fine for most folks. If they're open about having copied and marked as authentic, but not marketed as such...that's another. They're faking for the buyer and the buyer knows. BUT when the manufacturer and/or the seller conceals the fact that the expensive product is counterfeit they're duping the buyer and the public regardless of what they're charging and I can't understand anyone making excuses for that sort of theft.