I tend to try and give them the impression that I'm gullible enough to maybe fall for it, then say I quickly need to do an urgent thing like move the washing to

I tend to try and give them the impression that I'm gullible enough to maybe fall for it, then say I quickly need to do an urgent thing like move the washing to the dryer, put them on hold, and later check how long they stayed on the line, all hopeful that they may have found a victim. The record so far is almost a quarter hour. It's definitely the best target to optimise – the more time they waste on you, the less time they have to work on some poor soul who's actually vulnerable.