Joel with the straight dope:

…Next step: do not call the broker in the listing. Yes, they can show you the space, but you don’t need them yet. First go to the building in the listing and see if you like the building. Check out the lobby. Read the list of tenants to see if they’re mostly software companies, architects, and graphic designers, or if they’re mostly clothing factories, importers, and methadone clinics. Check out the neighborhood. In the bad buildings, people get into the elevators talking to themselves. In the good buildings, people appear to get into the elevators talking to themselves, but they have a tiny earphone, so it’s totally different, they’re just on the phone…