Mich. Comp. Laws § 566.135: Representation concerning character; business or credit of another.

Sec. 5.

No action shall be brought to charge any person, upon or by reason of any favorable representation or assurance, made concerning the character, conduct, credit, ability, trade or dealings of any other person, unless such representation or assurance be made in writing, and signed by the party to be charged thereby, or by some person thereunto by him lawfully authorized.