There's a bunch of services over the web providing verified reviews. But it has becomes a dangerous game to play in, Amazon are cracking down on such services, and consequently, on accounts which use them
If you have your own buyers setup and you know what you're doing, it may work out for you to do such a thing
But keep in mind Amazon is on their top game when it comes to any type of ⊗⊗⊗⊗ reviews/⊗⊗⊗⊗ buys. I personally do not recommend it, its better to just organically and naturally build positive feedback. Its a lot safer being the primary reason.