Firing an Agent

I assume you're a seller, with an agent you retained through a listing contract?  You always have the right to cancel an agency.  You may be asked for the agent's out-of-pocket expenses on your property, though.  To cancel an agency, contact the managing broker in that office, and ask for the form on which you can withdraw the agency.

If you're considering selling to someone who's seen the property while it was listed, though, better take a look at the listing contract and see if says anything about that situation.