A low price does not offset a warped shaft or hidden crack. Inspect in daylight, take your time and record the condition before paying.
Geometry
Roll each part on a true surface or watch the end while it spins. A slight deviation may be a model characteristic, but a kink, crack or delamination is a reason to walk away.
Joint and tip
Assemble the cue, tighten the joint gently and check for play. Inspect ferrule, tip and shaft end; fresh adhesive can indicate recent repair that needs documentation.
Provenance and value
Ask for serial markings, repair history and honest defect photos. Compare the price with a replacement shaft, tip and shipping. For a valuable cue, arrange an expert inspection or a protected return window.