Mich. Comp. Laws § 45.89

Sec. 9. When any bid shall have been accepted, the purchasing agent may require of the successful bidder, a bond payable unto the county with good and sufficient surety, in the sum of not less than 1/3 of the amount of the bid, to be approved by the purchasing agent, conditioned that he will fully, faithfully and accurately execute the terms of the contract into which he has entered. Said bond shall be filed in the office of the purchasing agent and recoveries may be had on such bond until exhausted.