The part-worn problem: where corners actually get cut
The used-tyre trade is where most of the genuine danger in this market lives. Part-worn tyres are sold cheaply from the back rows of industrial-area shops, often imported in bulk from markets where they were already retired. The problems stack: unknown history, possible internal damage from a previous impact, age often at or past the five-year threshold, and storage in shipping containers that bake in the sun for months. A tyre that spent a summer in an unventilated container has aged years in chemical terms. Municipal authorities have run repeated campaigns against non-compliant tyre stock, and this segment is the reason.
Your defence is process, not suspicion of everyone. Insist on seeing the removed tyre and the damage before agreeing to a repair-versus-replace decision. Ask whether the repair is a patch-plug from the inside. And when a puncture sits in the shoulder or sidewall, accept the replacement verdict: no honest fitter will warranty a repair there, and any insurer investigating a later blowout will find it.