On the first point, Amazon should strictly prohibit gifting free Vine items to others. It is inherently antithetical.
On the second point, no. I don't think it's possible to give free items to people and get honest reviews. The free-ness will often induce either charity or laziness in reviewers. The only way to get an accurate review on a product at its price point is to sell the item at its price point in the wild.
