First, they have to prove what SEO is and what is the purpose of links in this equation . . . Ask them to explain this to the judge before asking you any questions.
It will be fun to watch
Second, their lawyer would need cold hard facts from Google that says: "Yes . . . Link building will help you improve your rankings, bad links will do the opposite". Good luck getting Google to admit anything about that. Heck good luck contacting Google.
My point is there is no way you can lose a case for something that can't be proven.