When a troll launches a deception; post the facts. When the troll spins the facts or attempts a misdirection; post more facts pertinent to the original matter. Trolls run out of energy and enthusiasm for the game long before facts are exhausted.
If a troll can bring you down their level, exchanging personal vitriol, they'll usually win. They have much more experience with life in the gutter or under the bridge. Stay on the high ground, hold your nose with your left and keep pitching with your right until the odor subsides.
It's only fair to give them one last chance to come clean. It also gives them clear warning of what is to come if they shoot their mouths and I find their posts. As it is, the least that happens is that they run if I show up (as FO usually does). It saves me time to implant a little caution and cleans up the forum a bit in the process, or at least that is the intent.