After exchanging wedding vows, Maribel Garate (L) and Sherrette Estes look for a place to be alone before being introduced to their guests as a married couple at Glenview Mansion in Rockville, Maryland, in 2013. (Jahi Chikwendiu/WASHINGTON POST)

When Kathryn Hamm 10 years ago started running GayWeddings.com, a “mother-approved shopping site” for same-sex brides and grooms, chats with wedding planners, caterers and invitation-makers often devolved into awkward detentes.

“It felt like begging trying to convince them that same-sex couples wanted to have a ceremony, that they were an unserved market,” Hamm said. “Our litmus test was just if they were going to hang up on me.”

But amid rapid changes in America’s same-sex-marriage laws, Hamm’s small niche site has become anything but. In four years, the number of vendors who told the site that they were willing to help wed same-sex couples has exploded, from 20,000 to 120,000. On Tuesday, the site unveiled that it would be bought by WeddingWire, a Yelp-style online rating giant for the $50 billion U.S. marriage industry.

As same-sex marriages have surged into the mainstream, so too has the gay-wedding industry, now serving one of the matrimonial world’s fastest growing markets, which is a financial force all its own. Same-sex weddings could become a $2.5 billion industry if legalized nationwide, an analysis by financial data site NerdWallet shows.

Although same-sex ceremonies were once rarities, they have become an increasingly expected, and important, part of businesses’ bottom lines. Even in states such as Indiana, where a bakery this year made headlines for refusing to serve cake at a gay wedding, vendors have fought to capi­tal­ize on same-sex couples’ special days.

“My florists are used more. My linen vendors are used more. My event spaces are used more,” said Stephanie Rice, a social catering sales manager at the Conrad Indianapolis, a downtown hotel and wedding venue. “That’s more money. Who doesn’t like money?”

The growing social norm of gay marriage has made it harder for the competitive small businesses and entrepreneurs of the U.S. wedding industry to stay away. According to a Washington Post-ABC News poll in April, about 61 percent of Americans said that they support gay marriage, which is permitted in 37 states and in the District. This month, the Supreme Court is expected to make a decision that could legalize same-sex marriages nationwide.

A study by TheKnot.com, the country’s biggest wedding site, found last year that, although same-sex couples on average hosted smaller ceremonies, they still spent about as much as opposite-sex couples, about $200 per guest. Same-sex couples were also more likely to spring for a pricier honeymoon or to pay for their wedding themselves.

For many vendors, the struggle has been not about whether to serve same-sex couples, but how to compete with rivals for the couples’ business. At last year’s Wedding Merchants Business Academy, an annual conference for vendors in Las Vegas, speakers counseled attendees on practices for attracting business from same-sex weddings.

At the Conrad Indianapolis, Rice said she has spent hours helping redesign menus and marketing materials to make them less bride-and-groom-oriented, and she said she has gotten better at knowing what to ask, such as who wants to walk down the aisle first.

It has paid off, she said: The hotel has a half-dozen same-sex ceremonies planned for the coming months, including for one couple driving an hour from their home in Fort Wayne, Ind., for a 50-person ceremony in the hotel’s Vienna Ballroom.

WeddingWire, based in Chevy Chase, Md., has partnered with the Washington-based GayWeddings.com for years. But news of Tuesday’s acquisition made the pairing official, folding GayWeddings.com’s list of “LGBTQ-friendly wedding vendors” further into WeddingWire’s expanding hub.

WeddingWire, which had a revenue of about $49 million last year, has pushed to expand into a dozen countries in Europe and Latin America. But the GayWeddings move highlights how big the U.S. market has become.

“Everyone has a clear view of where [that market] is headed, and my sense is it’s growing at a faster clip,” said Timothy Chi, WeddingWire’s chief executive. But “there’s still a lot of education that needs to happen, as well.”

It’s a welcome change for same-sex couples who for years have, as Hamm said, gotten “used to filtering the straight world to get our needs met” on the wedding aisle and elsewhere. Increasingly, vendors will offer contracts designed for a “couple,” instead of a “bride and groom,” as well as planners, photographers and other professionals well-trained in non-traditional wedding rituals.

A.C. Warden, an ordained interfaith minister whose Capital Ceremonies leads weddings throughout the Washington area, said that the same-sex weddings she leads nowadays are often far different from years ago, when they were almost always small affairs, often involving travel to a different state.

Today, when she helps customize a ceremony for a couple, she often sees them using the same caterers, planners and party trappings as opposite-sex couples.

“It’s not hugely different. It’s two people coming together to create a life, to support each other,” Warden said. “It’s their marriage. They’re doing the hard work. I’m just facilitating the process.”