Nor is that the function of this forum.There is not nearly enough information to guess what the response should be.
My understanding of OP's initial post is that they were of the impression that the buyer should not have been allowed to file. They weren't asking "What should we do? How should we respond". Rather, they were affronted that something was filed, and thought that the man should have been magically blocked from filing.
Since obviously he did file, that is a nonissue. As Zig pointed out in post #6, a party can file a suit, even if they have no grounds.
The issue you have tried to point out is that they have to respond, they are shooting themselves in the foot if they don't; they are focusing on the wrong thing(s).
If they can't search "Responding to a 93A Demand Letter in Massachusetts" then their needs are beyond the scope of this forum.