Paperwork matters more than the part itself. A yellow tag, 8130-3, or equivalent traceability document is the difference between a serviceable part and an expensive paperweight your mechanic will refuse to install. If you're buying, ask for the documentation up front. If you're selling, post it in the listing — it dramatically increases the chance of a sale.

Condition terminology matters: 'new' means never installed and in original factory packaging. 'Overhauled' means taken to published overhaul limits by a certified shop. 'Serviceable' means inspected and within limits but not overhauled. 'As-removed' means pulled from an airworthy aircraft but not re-inspected. 'Core' means a rebuildable but currently non-serviceable unit.

Shipping high-value avionics? Use a box with rigid foam on all six sides, insure the shipment for replacement cost, and photograph the unit serial number before it leaves your hand. For cylinders and cases, palletize anything over 70 pounds.

For salvage buyers: if an aircraft was involved in a reportable incident, look up the NTSB record before purchasing parts from that airframe. Some parts may carry an airworthiness impact even if they appear undamaged.