When they start touring places, some will schedule or cancel appointments at the last minute.
While some stars are "lovely" to work with, others "don't always appreciate your time," she said.
"It takes a certain type of broker to be able to handle celebrities," she added. "They can only go out on Saturday. You'll go crazy trying to make the appointments on Saturday, and then they cancel half an hour before," she said.
Muss wouldn't name names. She said that often, in dealing with celebrities, she signs confidentiality agreements that stipulate that she can't reveal that they're working with her.
Real estate agents aren't mum all the time. Abelson said that some will leak news of celebrities to the press to attract publicity for their services.
Of course, some real estate agents treat their clients like family -- because they are. Johansson 's brother was her real estate agent, according to a New York Observer story by Abelson.
But the family ties attracted less attention than Johansson's selling price on her Tribeca duplex. The actress sold the apartment for $52,000 less than what she paid for it in 2006.
Johansson wasn't the only celeb to compromise on her asking price. Bon Jovi and actor Kevin Spacey both reportedly dropped the asking prices on their respective condos too. Bon Jovi sold his place in February.
If Johansson had sold the unit a year earlier, she might have avoided the loss, Abelson said. Still, he added, Johansson may have let the apartment go at a lower price because she could afford to.
Bono probably could have secured a higher sale price for his Central Park West apartment too, he said.
"Celebrities seem to have their own rules when it comes to real estate," Abelson said.
"In both cases," he said, "I think it's probably because neither of them particularly needs the money -- not because they were forced to sell because of the bad market."