I've floated this out there before, but I'll do it again...
I like to relate this to the guitar world.
Gibson has Epiphone, which basically makes knockoffs of their higher end guitars. Same with Fender and Squier. I have guitars and basses from all four. While all are quality instruments, the little things and attention to detail are much better on the genuine Fenders and Gibsons. Do the Epiphones and Squiers do the job? Absolutely.
Why do those manufacturers 'dilute' the market with these 'clones?' Because so many other companies were doing it. In the 70s the Japanese company Ibanez was making better Les Pauls than Gibson, I know, I had a couple. Gibson took notice, and eventually the importation was stopped, with many of them being destroyed by Customs.
In other cases, off shore manufacturers were selling their off production time to make instruments on the same lines with pretty much the same materials. I have a bass sold by Hohner that is in reality a Steinberger, just with Hohner and 'licensed by Steinberger' labeling on it. It came with cheaper knobs, wiring and strings on it, but all said and done, is the exact same instrument at a much more attractive price point. I have seen, owned and played other instruments that I am positive were produced in the same type of setting, but without the authorization and endorsement of whoever put the factory up.
On the other hand, there are thousands of Fender and Gibson 'clones' out there made from inferior materials that kinda sorta look like the real thing, but are sorely lacking in performance. But, they're not trying to pass them off as the real thing.
So is it possible or even likely that this is happening with mods and other gear? Absolutely. So if they're not legit, it's incumbent upon the original manufacturers to alert Customs that counterfeits, items infringing on patents, copyrights and trademarks are being imported. You should see the slick documentation provided to Customs by Disney - they are probably the most diligent about protecting their brands. They regularly produce and distribute lists and photos of counterfeit items being produced in China as well as who is producing and shipping them. These almost never make it into the country.