It's not a "direct" payment, but there's the carrot of "accomodation" pricing, by which well-audienced reviewers have the option to buy the product at a price (sometimes) below used market value. Then they have the additional boon of being able to cap a review like: "I enjoyed the SonicNinja Gaiden Hyper Mk XVII.a SE so much, I purchased the review sample!"
Even if they DON'T like the component, a well-spun review keeps open the option for future Products review samples which they might actually want.
You can stick a component in almost any system and hear a dfference - and 99% of the time, that difference can be spun in a "positive" light, with varying degrees effort. And don't forget to tack on the old trope comparsion: "it sounded almost as good as {well known high end component} at 10x the price!". When reviewrs introduce multiple variables at once (multiple review products at the same time) this just adds to the chaos.
Professional reviews are for entertainment value only - they're not a reasonable guide for building your own system.