One of the cardinal rules of selling real estate is to not market a fellow broker's exclusive listing as your own. And it looks like that rule's being broken on one prominent Hamptons property. One astute reader discovered that Stribling agent Jessica Mansell Ambrose has been calling Christie Brinkley's $30 million Bridgehampton estate her exclusive on her Web page. (According to that page, that's the only active listing Ambrose has.)

"That's news to me," Brinkley's exclusive Corcoran Group broker, Susan Breitenbach, said. A short time later, Breitenbach called back and said it was also news to Brinkley that Ambrose was hawking her Tower Hill property.

Our source said that Ambrose is a friend of Peter Cook, Brinkley's ex-husband to-be. And it might have been Cook who had given his permission for her to put the house on the market. But there's one small problem: Cook is not an owner of the 21-acre compound.

"All I know is that I have a signed exclusive contract with Christie and that I'm spending a lot of money advertising the property," says Breitenbach.

When we reached Ambrose via e-mail, she insisted she is not the exclusive broker for the property. But her Web site had not been changed as of press time.