Termite inspection of a home?

We have a home for sale. We have a potential buyer and he had a termite inspection done. First, they said it was full of them and then it was well there was damage but their estimate to treat the house was ,200. He said it has to be treated or he will not buy the house. My question is, how do they do termite inspections? We had some remodeling done last year where they tore into the walls. They said they found evidence of them in the past but no live ones. And now a company says it's full of them? I know they can come back but I was just wondering how they check for them without tearing into walls etc. The estimate was ,200 for a small house. We are going to get other estimates of our own.

View this post on my blog: http://madeinhome.info/termite-inspection-of-a-home