“Shill” | /ʃɪl/
n – A person paid to endorse a product favorably, while pretending to be impartial.
“Acting as a shill for the company, Laura put fake reviews online as a way to get others to buy the products.”
v – To promote or endorse in return for payment, especially dishonestly
“He was hired to shill the new product, even though it wasn’t considered safe.”
Unknown; attested as verb 1914, as noun 1916. Perhaps an abbreviation of shillaber, attested 1913. The word entered English via carny, originally denoting a carnival worker who pretends to be a member of the audience in an attempt to elicit interest in an attraction.
Speculatively an extended form of German Schieber (“black marketeer, profiteer”) via *shi-la-ber.