sure that happens - on Amazon's scale, does it matter? As a consumer, I like a few honest reviews vs thousands of reviews that contain useless/dumb/rant type reviews. I'd have to weed through those reviews to find honest ones which takes time and energy, and ultimately I'd just give up - which defeats the purpose of reviews in the first place.
But if you still want to address this problem, just allow the buyer to say it is for someone else and allow them to put the recipient's email. If I buy something for you, I put your email, and Amazon could allow you to review the item instead of me reviewing it.
Once you take a turn off the mainstream there are thousands of products on Amazon without any reviews. People therefore appreciate any information whether it was bought from Amazon or outwith.
But if you still want to address this problem, just allow the buyer to say it is for someone else and allow them to put the recipient's email. If I buy something for you, I put your email, and Amazon could allow you to review the item instead of me reviewing it.