Mainly, soil poisoning. Yes, it takes experience and expertise - so make sure you get someone that's been doing this, on YOUR type of house, for a long time. Best chemical, today, is Termidor. Premise is almost as good. Opt out of termite baiting or the application of any chemicals directly to the wood.
Some exterminators also push wood treatments of one type or another.
I think, in most every case, these are worthless add-ons. That method is soil poisoning. We have never treated a house, entirely, with a bait system. I'd spot-treat it and give him my honest estimate of what he might expect, and what to do about it. After all, if he does get termites somewhere else, I want him coming back to me.