What types of trailers need to be inspected in Maryland?

Certificate of inspection

A safety inspection is required for all used cars, trucks, tractors, trailers, motorcycles, special equipment, and class “B” for hire vehicles being titled and registered in Maryland. They must be inspected by a licensed Maryland inspection station, such as an automobile dealer, service station and specialized automobile service center. A certificate of inspection, issued within 90 days of the vehicle to be titled, must accompany the application for a title. Please compare the vehicle identification number (VIN) on the inspection certificate with the one on the vehicle and the vehicle ownership documents to make certain they all agree. Altered inspection certificates will not be accepted.

If you purchase a used vehicle and cannot transport it to an inspection station to have the vehicle inspected, you may request a 30-day temporary registration when you title your vehicle. To apply for the temporary license plate, you must complete a temporary inspection waiver (form #VR-129). There is a fee for the temporary registration.

Credit:
https://mva.maryland.gov/vehicles/Pages/registration/title-registration-info.aspx#certinspection