Decades ago, your vacation most likely began with a visit to a travel agent, who relied on a combination of expertise and connections to find the best deals on plane tickets, hotels, tours and more. Since then, the internet has turned most of us into our own travel agents, and artificial intelligence software is making research and self-booking even easier. But for some trips, that special insider knowledge can still make a big difference.

So when should you hire a professional, and how does it all work? Here are some tips.

Why should I consider a travel adviser?

It’s easy for a traveler to do the research for a standard trip, said Chris Anderson, a professor at the Cornell University School of Hotel Administration, “so they should look for a specialist for the type of tour they are looking for, say a bike trip in Ireland, who can really add value.”

The insider knowledge offered by a travel adviser can add the most value to trips that have multicity itineraries, involve a wide age range of travelers, are very significant (like an anniversary vacation) or are to destinations you are unfamiliar with, said Gary R. Johnson, who has run the travel agency Woodside Travel in Seattle for nearly 30 years. An adviser could help you decide, for instance, in which order to visit European cities based on local events and transportation options.

What can an adviser give me that a booking site can’t?

Travel advisers can help you research the best destinations, lodging, or activities for your particular group and travel goals, offering up specific advice that might be hard or time-consuming to find yourself. Those specializing in cruises might know which cabin to choose if you are prone to seasickness, while a safari planner could help you decide which park would be best for bird-watching or seeing specific animals, like rhinos.

Travel advisers typically have relationships with tour companies, hotels and cruise lines, sometimes through networks. Those connections can allow advisers to offer extra perks such as late checkout, free breakfast, airport transfers, a welcome basket or a credit to spend on a cruise ship.

“A good travel agent will be a better steward of your travel budget than you are,” said Guy Rubin, managing director of Imperial Tours, which arranges travel in China.

When bad weather or other circumstances disrupt your itinerary, travel advisers often have direct lines of communication with providers and can do the work of rebooking and changing plans, saving you time and stress.

OK, let’s say I need help. How do I find an adviser?

Networks like the American Society of Travel Advisors and Travel Leaders have websites that can help you start your search for a travel adviser by answering a few questions about your desired trip. Once you have a handful to choose from, get on the phone with them to talk about what they might do for you, how they charge and the level of service you can expect. Special trips can cost thousands of dollars, so it’s worth investing time up front, Mr. Rubin said.

Make sure to read over the travel agent’s reviews and any user-generated social content that mentions them, Dr. Anderson said. “If there is no external validation, that’s a red flag.”

How do advisers get paid, and how much will it cost me?

Advisers receive commission from suppliers, typically 10 to 15 percent of the price, when selling cruises, lodging and tours. They also sometimes charge travelers a planning fee, from a few hundred dollars, which may be credited to the final bill if the booking is completed, all the way up to tens of thousands of dollars annually for a luxury concierge travel planner they can call on all year. Mr. Johnson said that he charges a planning fee the first time he works with customers. If they return for other trips, he waives the fee.

Advisers may be tempted to sell you something that will earn them a higher commission, Dr. Anderson said. But, he points out, the same is true for the large online services, which promote hotels that pay them larger commissions. Travelers can ask advisers about specific commissions they receive or how they are affiliated with the products they are recommending, he said.

Sometimes a local tour company will package transportation, lodging and experiences for an adviser, who tacks on a percentage before passing it along to a client. But a bill that is not itemized can make it harder to make trade-offs — between a more expensive hotel and a special experience, for example. If pricing transparency is important to you, discuss it with the adviser up front.

How are A.I. and other technologies affecting travel advisers?

While new technologies are allowing do-it-yourselfers to create their own itineraries online based on individual preferences, and to type questions directly into travel websites, advisers are also taking advantage of those technologies to improve their services. Joan Roca, chief executive of the upscale travel planning company Essentialist said his team “uses technology to enhance the human touch,” employing artificial intelligence to choose options from a database of travel offerings selected by a human team. If a couple wants to take an after-dinner stroll, for example, Essentialist’s app will offer up ideas of where to go, based on what part of the city the travelers are in and conversations they’ve had with their travel adviser.