When evaluating flat deck trailers, the most critical factor is the load capacity (payload), which typically ranges from 20 to 60 tons for standard B2B applications. You must verify the main beam material, prioritizing high-strength Q345B or T700 steel to ensure structural integrity under heavy stress. Additionally, check the axle brand and capacity (e.g., FUWA or BPW 13-16 ton axles) and the braking system, where a WABCO relay valve is the industry standard for safety. For the flooring, 3mm to 5mm checkered plate is recommended for anti-slip performance.