Shill
[A pharma shill is a person or group selling or promoting drug industry products while claims to be independent and doing it purely because it is the best available product.]
"A shill is an associate of a person selling goods or services or a political group, who pretends no association to the seller/group and assumes the air of an enthusiastic customer. The intention of the shill is, using crowd psychology, to encourage others unaware of the set-up to purchase said goods or services or support the political group's ideological claims."--Wikipedia