The agent doesn't give honest, specific advice.
In a slow real estate market, you have to employ all the right tricks to sell a house, and this may include some very specific home improvements. The advantage of having an agent to help with the sale is that the agent should know how to apply all the right tricks to your property and should be able to give you honest, specific advice about the improvements that will help sell your home.
So if you're interviewing an agent, and you don't hear anything a little bit painful about changes you need to make to prepare your home for sale, be wary. An honest, knowledgeable agent is better than one who just tells you what you want to hear.