Turns out, the neighbourhood also had hate.
A woman lounging at the pool took one look at his client's hijab and said it loud and clear: "We don't want Muslims in our clubhouse. Take off that robe over your head!"
Carlos, 44, was flummoxed. He wanted to confront the woman, but didn't want to cause a scene. He instead went to the clubhouse manager, who was equally horrified by the outburst and apologised, frantically explaining that the woman does not represent her diverse community.
The couple, who were used to such attacks, were gracious about the whole thing. They're still house-hunting in Frederick.
But this is not where the Herboso brothers' story - or their shock - ends.
Islamophobic attacks and other hate crimes are spiking sharply in the United States, especially since Donald Trump began suggesting that America ban all Muslims.
Data from the FBI said that in past years, there have been a little more than a dozen suspected hate crimes against Muslims reported every month.
But since the attacks in Paris and the ramp-up of American nationalist rhetoric, including Trump's suggestion that the country create a nationwide registry of Muslims, that rate has roughly tripled.
Fernando Herboso glimpsed the change in sentiment a few months ago. He was showing a different Muslim family a house, also in the Maryland suburbs. Their young daughter needed to use the bathroom. The water had been turned off at the house, so Fernando went to ask a neighbour who was outside gardening.
The woman glanced over Fernando's shoulder, and saw the family, wearing traditional Muslim garb. She wordlessly turned her back to him, went inside her house and - click - locked the door.
"What do you tell your clients when something like this happens, when you want them to find a neighbourhood that is safe and welcoming?" Herboso said.
He posted something on a real estate agent's forum, wondering whether others have seen an increase in such bold displays of bigotry and whether they thought it was a new division in the country sowed by Trump's politics.
What he heard back, he said, was "disheartening". "My post somehow gave my colleagues in real estate permission to reach out to me with hateful comments about my Hispanic heritage," said Herboso, who was born in Bolivia. "I never experienced that before. I arrived to the US in 1977 and have been a proud American since 1982."
In 25 years in real estate, many running his own company, he never felt discriminated against. He shut anyone down with hard work and his effusive love for America.
And suddenly, he was being attacked by agents he saw as his peers. Guys who bantered listings with him fired off nasty emails and even made phone calls urging him to go back to his country.
What do you tell your clients when something like this happens, when you want them to find a neighbourhood that is safe and welcoming.
"I don't even know what Hispanic means. Are you from Spain, Mexico, Argentina, Guatemala, Cuba? Does it really matter?" A fellow Realtor lashed out at Herboso. "I have to assume that it refers to some culture that you relate with that is different than the American culture. But what do you put first, Hispanic or American?"
It felt, he said, "like they were wearing masks all these years and they just took them off".
He got private emails, too, suggesting it was fine for neighbours to want to keep Muslims off their blocks.
"Really, in this day and age, who among us would not be a bit worried about a Muslim moving into our community," a colleague wrote to Fernando. Here is the part that was so shocking to both Herboso brothers - the silence they misunderstood for decades.
All these years, it wasn't untainted friendliness. It wasn't a happy rainbow. It wasn't about those key words: "We hold these truths to be self-evident, that all men are created equal." It was racism and scepticism and hatred all along, Fernando said.
"I remember coming to DC and riding the Metro. And I wasn't a Hispanic on the Metro. I was just a person next to someone Chinese and someone Indian and someone Mexican. And we were all just people on the Metro." And now, "I have to think that the racism part was always there," Herboso said. "But it was silenced."
He's worried not just as an American, but as a parent.
"I have a son, he is 8," Fernando said.
"I don't want anybody to look at him like he's illegal. I want them to see him as a person. As an American."
