This just came to my attention recently. I noticed one of our products dropped in numerical ranking quite a bit (Dropped from a 4.8 to a 4.6), and I couldn't figure out why since we didn't have a lot of reviews come in on that one recently. I dug a little deeper, and realized that ALL of the reviews we by people that we gave big discounts to ($1-$2 per product) lost their "verified review" status, and all of these purchases and reviews are NOW classified as unverified.
This status is critical, because it shows prospective buyers that people actually bought the product from Amazon and used it. It is nearly impossible to prod a full price buyer to leave a review unless they are angry at you (we get far less than 1% of the people that buy at full price to leave a review). Additionally important, is that Amazon gives greater weight to verified reviews in the rankings as well as their value in the overall product rating.
So it looks like a major sea change on their part to discount the value of these reviews. If you read Amazon's verified review standards, it now states that products purchased with a "deep discount" will no longer be considered verified. It also looks like they went back and retroactively unverified all the previously verified reviews. Hence the immediate loss in ranking of this particular product.
First of all, this stinks because of everyone here that has put so much effort in reviewing products, and of course the loss that is absorbed for merchants to give discounts. Aside from that, some kind of solution needs to be found going forward so reviews still have some kind of value for both sides.
I would ask merchants, anecdotally speaking, what level of discount percentage can you offer a reviewer for product so it doesn't qualify as a "deep discount" by Amazon's standards so the review can still be verified? This is something we all need to pay attention to going forward.