If you buy stolen property, the only recourse you have to get your money back is from the person who sold you the property, who would probably be long gone or impossible to sue. The rightful owner of the property does not owe you anything. Plus, how do you prove to the rightful owner what you actually paid? Do you think the person who sold it to you will give you a receipt or allow you to pay by check?
The rightful owner of the cue can appear at anytime and prove it's his and you will have to turn it over, regardless of how much time has passed or how hard you looked for the owner. Then you become a suspect, even if it's just by rumor only. Do you want rumors like that circulating around about you?
I think the best thing to do is not to buy the cue, but pass the word around that the cue is in circulation. Take a photo of it with your phone if possible and post it up or send it around.