I make roughly 150 Amazon purchases a year. The only “counterfeit” (and I use the term loosely) product I’ve ever gotten was a knock-off electric toothbrush head from a third party seller. It wasn’t passed off as being from Oral-B, and it did fit the toothbrush— it just didn’t work very well.

I chalked it up to a life lesson. Other than that, never had an issue.