The agent doesn't return phone calls.
Granted, this is an obvious bad sign, and it's the first of many you may see if you're in a contract with an agent who's overwhelmed or disorganized.
The key here is that you should be able to see this coming to some degree.
If you've made the effort to interview two or three agents before you signed a contract, then you've already seen how quickly most agents return messages and how well they listened to your concerns.
Like professionals in any business, you can see a real range of behaviors from the outset. While one agent may return a voice mail after a couple of days and engage in a matter-of-fact conversation, another agent may answer the phone on the first try and then send a thoughtful letter to follow up the next day.
It's like hiring anyone for any type of job, whether it's roofing, babysitting or bookkeeping. But this hire involves getting the best return on the biggest purchase you've ever made.