Every seller asks that question and every agent gives an answer and usually the agent that gives the highest price gets the listing and doesn't get the house sold.
So sellers should ask agents to give them all the information they need to arrive at a compelling price for their home. When trying to determine a price that will attract the largest buyer pool for their property it is critical that sellers pay careful attention to properties similar to theirs that have recently sold!
Be wary of the agent that gives you an inflated price to entice you into listing your home with them. Your house is worth what a buyer will pay, and buyers pay what other buyers seem to be paying for similar homes. An agent can tell you what has recently sold and they can give you their opinion of the value of your home, but that is just their opinion. Always rely on the facts that are presented to you and when possible visit the agent in their office and have them go online to show you those facts.
Today buyers have more pricing information available to them than they ever had before. They can go on several sites and get an on-line evaluation of any home. This information is based on recent sales of similar properties and not on what an agent thinks.
The best way to determine what your home is worth is to review the recently sold homes that are most similar to yours and then pretend you were buying the house and ask yourself what you would pay for your home based on that information.