When sourcing a used low bed trailer, you must prioritize the load-bearing capacity and structural integrity. Check the main beam material (typically high-strength Q345B or T700 steel) for any signs of welding repairs or cracks. Verify the axle brand and condition (e.g., BPW or FUWA), as these are critical for heavy-duty transport. Additionally, inspect the tire wear patterns, which can indicate alignment issues, and ensure the hydraulic ramps (if applicable) operate smoothly without fluid leaks.