I would say "冒牌"- fake brand, is closer to 做媒 in Cantonese, except while it means the "matchmaker".
他是冒牌的 and 他是冒牌貨 both mean "he is a fake...." for the purpose of enticing sales, or carrying out a scam by faking his identity.
Unless the meaning has been expanded, in Mandrin, 托儿 means putting a child under someone/someplace (...
Maybe, 托儿(read as 托r, not the one in 托儿所） is the one you are looking for? It's someone who helps lure customers into buying.
This use of 托 is relevant to the sense of 烘托 and 衬托(serve as a foil). E.g. 我衬托你 means I serve as a foil to you. So, 托儿 serves as a foil to 商家 in this case to promote products by pretending to be a real customer and etc.