If you want to protect your interests, beyond just this domain, talk to a lawyer.
Otherwise, talking to a broker may not be a bad idea - if you listen. For instance, they may advise you to sell for a price that reflects risks and costs of litigation/UDRP.
OTOH, if the domain is truly generic (see if there's other trademark applications for the use of the same word(s)) and you haven't otherwise taken steps to trade on their alleged brand (what you've indicated) AND you haven't said anything in email or phone calls that could be used against you in a court of law or legal proceeding you might hold onto it or have a better bargaining position.
There's a lot to consider, which is why talking to an experienced IP lawyer is the only sensible way to sort out what to do. Unfortunately, people who can afford to register a domain are often the same people who cannot afford to consult a lawyer.