Most of the time I'm gentle with those callers. There isn't a single one of them who's doing it by choice, and they work under des picable conditions for crap pay. I politely say "not today, thanks" and hang up.
The exception to my rule are the weasels selling penny stocks, diamonds, krugerands and such. These guys ARE doing it by choice and potentially making excellent money suckering people. When they call, the gloves come off.
They're depending on a very small percentage of suckers falling for their scam. The longer I can keep them on the phone, the fewer victims they'll claim that day. I've kept them on the line for over an hour. Tell me more, I'd say, then make a cup of tea or get on the forum while they entertained themselves with the sound of their own smug voices.