shill

Short definition from Wiktionary

Noun

1. 1
   A person paid to endorse a product while pretending to be impartial.
2. 2
   Any person enthusiastically endorsing a product; especially, one who is getting paid for the endorsement.
3. 3
   An accomplice at a confidence trick during an auction or gambling game, such as an accomplice of the seller who bids to drive up the price.
4. 4
   A house player in a casino.

Verb

1. 1
   To promote or endorse in return for payment, especially dishonestly; sometimes extended sarcastically even to those not paid but strongly biased in favor.
2. 2
   To put under cover; to sheal.
3. 3
   To shell.

Proper noun

1. 1
   A surname.