Foxtons claimed it was entitled to a fee of £20,000
The Court of Appeal has ruled estate agency Foxtons is not entitled to commission for a house sale despite having shown the buyer around it.
The buyer decided not to buy the house when he first saw it because it needed too much work doing to it.
But when he was later contacted by another estate agency, Hamptons, he changed his mind and bought it.
The judges ruled that Foxtons needed to have "introduced the purchaser to the purchase" and not just to the property.
The ruling could change the way that joint agency agreements work.
But Peter Bolton King, chief executive of the National Association of Estate Agents, said it may just lead to a change in the small print.
"I think what it'll mean is a slight looking at some of the wording that is used in the standard terms of agency," he told the BBC.
"I'm sure this is something we will continue to work with the Office of Fair Trading on, just to make sure that everybody is very clear as to what they are signing up for."
Foxtons won its original claim for the £20,000 commission at Kingston-upon-Thames County Court, before it was overturned by the appeal court judges.