Inspect the Frame for Cracks, Dents and Deep Rust

Frame damage is the one fault that can make a bike worthless, so give the frame the most time. Work around it in good light, with a flashlight for the shadows, paying closest attention to the head tube, the bottom bracket, the seat stays and every weld. Paint that has bubbled, lifted or cracked in a line deserves a close look, because paint cracks often follow a crack in the frame underneath. Aluminum tends to crack rather than bend, and the cracks can be very fine. On a steel frame, treat rust that goes deeper than the paint as a reason for a closer look or a workshop's opinion. A crack anywhere, or a dent in a frame tube, is a reason to walk away, whatever the components are worth.