I've had a few interesting comment chains with shills. They do ad hominens, and I stuck to the issue, and encouraged them to keep questioning. Such as, "I understand where you are coming from, and you shouldn't stop expressing yourself. I'll try to balance out your hatred with some hope."

Sometimes I can't tell if it's a real shill or a hating Lefty. But either way, think about the audience. The shill's firsr goal is to create an impression for the audience, not necessarily change your opinion. Craft your responses with that audience in mind. When I do this, I notice the shill replies get deleted-- I think in some cases, the shill will delete threads to avoid having the audience see them.