I never had a problem (that I know of) with fakes on Amazon. I did cancel my prime membership and switched to Walmart. I feel like prices went up and quality went down. I wish I could move stuff away at work, we spend millions each month on AWS.
Here's a screenshot (not in English but easy to understand what's going on): https://i.imgur.com/hRJIiKk.png
The first one has 1.5k votes and 1.5/5 stars. If you get into the commets to see what's wrong you will see it's a fake. It's a M4 Smart Band, nothing to do with the Mi Band 4.
The second one has 2.5/5 stars and looks like people are receiving also a fake.
The others look good but who knows. All of them are from 3d party sellers.
Now I can buy the Mi Band 4 from Aliexpress for 36 euro (33 if I wait for a promo in 3 days) and I can be 100% sure that I'll receive the original one within 2-4 days. I can also buy it a bit cheaper from China but delivery takes longer.
I can give you another example. I want to buy a bag for my laptop. Almost everything I see in Amazon is from Aliexpress but more expensive.
Just save yourself the headaches and skip Amazon, where you have no recourse, for Home Depot, Best Buy, Target, and even Wal-Mart. Everybody does price matching these days.
If you're buying something you know is cheap junk, then just cut out the middle man and again skip Amazon for Ali express or Alibaba like the parent mentioned.