Md. Code, Insurance § 10–605

(a) Except as provided in subsection (b) of this section, an insurance policy sold in connection with, and incidental to, the rental of a vehicle under the provisions of this subtitle is primary to any other valid and collectible coverage.

(b) Any insurance sold to a renter under the provisions of this subtitle is not primary to the coverages provided by the motor vehicle rental company on the rental vehicle under § 17-103(b) of the Transportation Article.