Why don't you just use the product then write a real review. I do this all the time because I am writing a real review be it good or bad. Nothing wrong with writing a review of a product you sell as long as your honesat. If the product is a good product then you know it is worth keeping it it is a bad one well then ya know it won't be worth investing in and you can use this method to weed out the bad ones.
Oh and I ask the maker to send me one to write a review. Most of the time they are happy to do this and I get the product free of charge and write the review.
I get companies all the time asking me to add them to my site my first response is send me samples/product to test and I will then write a review of the product. Great way to test new items to see if they are worth adding. You would be suprised at the gems you can run across you have never heard of before that turn out to be great sellers.