I usually give them an honest chance. I think over the years I've had one or two that were marginally useful. Most of course are of the type "let me run search on what you typed on the background and regurgitate links to site's pages that match". Or fixed menu ones like "if you have $NOT_MY_PROBLEM, press 1, if you have $ALSO_NOT_MY_PROBLEM, press 2, otherwise press 'tough luck'".
I have the Drift widget on my site and a decent chunk of people seem intent on trying to figure out if I am a bot or a person. I haven’t yet come up with a sure-fire way to prove personhood quickly, so we can move onto their actual questions.