A used set can suit home practice, but uneven wear changes rebound and roll. Inspect balls individually instead of judging the set by overall shine.
Roundness and finish
Roll each ball on a clean, level table and compare its line. Dents, chips, cracks and heavy frosting are reasons to pass. Deep scratches can damage cloth.
Complete, compatible set
Match quantity and markings to the discipline: pool, snooker and pyramid use different sets and sizes. Do not mix series in competition without checking diameter and weight.
Cleaning and price
Ask for pre-polish photos and the cleaning product used. Compare the price with a new set plus replacements for the worst balls. Buy only with an inspection or return option.