They're not necessarily fake, but they may be incentivised. I've had offers of a £5 voucher for a photo review or £10 for a video (the product was a £15 solar panel). No idea what happens if you slate the product, but amazon would probably refund you if it was that bad.
Sellers are well aware how much of a boost a photo or video from a verified purchase can give.
Sellers are well aware how much of a boost a photo or video from a verified purchase can give.