To tip or not to tip, and if yes, when and how much for what services? For many travelers, the rules, if any, are murky. How much to tip often depends on the circumstance, and there are many opinions on the matter. So we asked a panel of travel experts for guidance. Keep in mind that these “tips” are only for domestic travel; tipping customs vary overseas, and there are no hard rules as to amounts. As Wendy Perrin, a columnist for TripAdvisor.com says, “I’m not a fan of giving somebody a tip just because they came to work. Shouldn’t tipping be to reward good service? And shouldn’t the amount of a tip vary depending on the quality of service received?”

Our expert panel: Sarah Schlichter, senior editor of IndependentTraveler.com; Wendy Perrin, editor of WendyPerrin.com; Ed Perkins, contributor, SmarterTravel.com; and William D. Frye, Ph.D., associate professor, College of Hospitality and Tourism Management, Niagara University.

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AT THE AIRPORT

A rental car shuttle bus driver: Perrin says it depends what they do for you. “If they help with a heavy bag, maybe $1 or $2.” Perkins suggest $1 and Frye would pay $2 per person for parking lot shuttle drivers but only “if they assist with luggage.

A skycap: Perkins suggests $2 for one bag, $3 for two and Perrin $2 per bag. Frye is more generous. “If they check luggage, $3 to$5 for the first bag and $2 for each additional bag, depending on how heavy. For red caps who assist at baggage claim, tip $5 for the first bag and $3 to $5 for each additional bag.”

A wheelchair attendant: Perrin says it depends. “How long did they accompany you, did they work on a holiday?” Perkins tips $2-$5 depending on time and distance, but Frye suggests $5-$20 “depending how long they spend assisting. Courtesy and promptness should also factor in.”

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AT THE HOTEL

A hotel maid: There was a wide range for this essential employee. Perrin says it “depends how big a mess my kids have made. Perhaps $5 to $10 a day.” Perkins tips a flat $2 per day and Schlichter $2 to $5 per night, “depending on how messy your room is.” Frye also suggests $2 to $5 per night, but “double if the room is a suite.”

A hotel employee who brings ice, an iron, or whatever to your room: Perrin thinks no tip is necessary “unless he or she had to go to great lengths to procure the item (e.g., had to schlep to a local mini-mart) while Perkins always proffers a flat $2.

A concierge who makes a restaurant reservation for you or provides another service: Perrin says there’s no hard rule. “It depends how much of his time you took up, whether he got you the reservation because you couldn’t, whether the restaurant was sold out, etc.” But Schlichter advocates “$5 to $25 for a concierge who has provided personal service.” Frye also says it depends: “$10 for simple tasks and it goes up from there depending the service.”

A bellhop who delivers bags to your room: Perkins and Schlichter propose $1 to $2 per bag, but Perrin says it depends on how far your room is from the front desk, how fast the bags are delivered, and how many bags you have.

A hotel doorman who helps you into a cab: Perrin: If that’s his job, nothing, but she’d pay $2or $3 “if it’s raining and cabs are hard to find.” Frye says “if they unload or store your luggage tip $5 for the first bag and $3-$5 for each additional bag and $2 to $3 more if cabs are hard to find.” Schlichter recommends $1 to $3 for a hotel doorman assisting with securing a cab.

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ON THE GROUND

A taxi or Uber driver: Schlichter says, “Part of the appeal of Uber is that you don’t need to tip, but you can if you like (in cash), and there’s some evidence that you could get a higher rating from your driver if you do.” Most of our experts suggest the standard 15 percent to 20 percent.

A tour guide: Schlichter advises that, “Museum guides do not need to be tipped, unless it’s an exceptional tour. For half- or full-day tours, tip $5 to $25 depending on the length, quality and cost of the tour.” Frye gives tour guides $3 to $10, with the higher amount for a small-group tour. Perkins offers $3 for a half day, $5 for a full day. True to form, Perrin believes “it totally depends on the circumstances. Is it a large-group tour? Small-group tour? Private tour?”

A coach driver: Perrin, who likes to be left to her own thoughts, quips “the less a bus tour guide talks, the more I’d tip him” while Perkins tips “$5 to $10 for one day, less per day on longer tours” and Schlichter advises $5 per day for the driver and $8 to $10 a day for the guide. Frye thanks tour bus drivers with a $3 to $5 per day gratuity.

Who NOT to tip: Does every one you meet while traveling deserve a tip? Our experts don’t think so. Our panel agrees that one would never tip flight attendants, airport check-in agents, TSA agents, airport club-lounge agents, airport gate agents, airline pilots, car rental agents, and especially not, says Perrin, “the hotel bellman who wheels my carry-on (despite my objections because I’d rather keep hold of it myself) to the front desk.”

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(George Hobica is founder of the low-airfare listing website Airfarewatchdog.com.)