middleman
noun [ C ]
uk/ˈmɪdlmæn/ us COMMERCE
a person or company that buys goods from the company that has produced them and makes a profit by selling them to a store or a user:
You can lower the price if you cut out the middleman and buy directly from the factory.
COMMUNICATIONS
a person who communicates or makes arrangements between two people or groups who are unwilling or unable to meet or deal directly with each other:
Generally, any unsolicited offer to make money by being a middleman for a transaction for somebody you don't know is fraudulent.