I have a Braun electric razor and needed a new 70S shaver head. There are plenty on eBay; some are advertised as compatible and sell from around £7.00 up, and some are presented as genuine Braun parts and sell for anywhere between £18.00 and £60.00 (the price from a Braun UK dealer is £45.00).
I am sure that some of the Braun spare are genuine but I purchased one I that was a counterfeit. How can you tell? First, it fits well but doesn’t give a good shave, it tears at your skin, showing that the engineering and manufacturing detail does make a difference. Second, there is no serial number on the inside of the shaver head (I am not saying all the counterfeits lack this, but it was the case with mine). Third, there are tiny springs in the original that were missing in my counterfeit.

It is not easy to tell from the outside though. There are small differences in the packaging and printing but one would expect some minor variations; both say “Made in Germany.”

Here is a close up of an original showing the small springs that are missing in the counterfeit, and the product numbers:

My seller was very reasonable about the issue and refunded me in full. However the part is still on sale.
It is good for competition that channels like eBay and Amazon exist; and the Braun shaver heads do seem expensive relative to the price of a new razor. I wish though that these platforms cared more about counterfeits as they are not only infringing on the rights of the original manufacturer, they are also a poor buy.