Would you like to upgrade?

On airplanes, do you ever wonder how the college-age girl in nondesigner jeans afforded that first-class seat?

How about the ill-suited man in scuffed shoes who nabs the top-floor suite at a hotel?

In many cases, they paid heavily for the upgrade or cashed in loads of frequent-flier miles or loyalty points. But those others? They worked the system.

To unlock the secrets of free or discounted upgrades for planes, hotel rooms, rental cars and cruise cabins, we went to industry experts and frequent travelers. Here are their tips:

Airline upgrades

•Use the upgrade certificates airlines send you for being a frequent flier, or ask friends holding transferable coupons with looming expiration dates if you can take them off their hands.

•Though airlines most frequently award their elite passengers upgrades, it never hurts to be the first in line at the gate counter and inquire about a bump in class. (Ask the gate representative, not the check-in agent, who does not control domestic first-class seating assignments.) Depending on the rep’s mood and the circumstances, the bump in class could be free – or, at the very least, less expensive than if you had originally booked the top-tier seat.

Alternately, don’t be the first to board. Hang back in case economy seats are needed and there is extra space in first class; you just might be offered that elite seat.

•If you have a flexible schedule and your flight is overbooked, volunteer to give up your seat and ask the agent if you may have a first-class seat on the next available flight.

•To increase your chances of flying in a higher class, book flights on wide-bodied planes, such as the 747 or 777, which have more first- and business-class seats. Check Seatguru.com (www.seatguru.com) for plane configurations.

Rental car upgrades

•Book the car by phone and ask if an upgrade is available. If it’s not, ask the rep to make a note in your record, then remind the clerk of that notation when you pick up the car. If one is available, it should be yours at no extra cost.

•Reserve the rental car location’s most popular model (ask when booking; most likely it will be an economy Ford). If the car is sold out when you arrive, you probably will receive a free upgrade – but remember, the larger car will guzzle more gas.

Hotel upgrades

•If you visit one city repeatedly, stay at the same hotel and befriend the front-desk staff. Upon check-in, mention that you are a frequent guest and politely ask if an upgrade is available.

•If you are staying for a single night, be bold and ask for a free upgrade. It’s just for one evening.

•For a weekend or holiday trip, book a room at a hotel in the business district or one popular with business travelers. The higher-end rooms probably will be empty during this slow period, and the front desk may be more willing to upgrade you gratis.

•If you are planning a meeting, family reunion or party, negotiate upgrades as part of the contract.

•If your hotel stay coincides with a birthday, anniversary or celebration, inform the front desk of the special occasion and ask for an upgrade.

Cruise upgrades

•Work with a cruise specialist. Forging a personal relationship with an agent can garner many perks, including cabin upgrades.

•Use the cruise line’s guarantee program. You reserve an inside cabin at the lowest price available and the cruise line guarantees at least that category’s lowest level of cabin; however, the line often says it will try to assign a better cabin within that category. (Upgrades from one category to another are rare.)

•Cruise during off-peak times in popular seasons. The Caribbean, for example, is teeming with ships during winter, but the period between Thanksgiving and Christmas and the first few weeks of January are the least in demand.

•Once onboard, register with the purser for an upgrade. The line will accommodate you if possible.

Upgrade tips

•Go online. E-newsletters from such travel Web sites as Travelzoo.com (www.travelzoo.com) and Sidestep.com (www.sidestep.com) alert travelers to upgrade specials; Car Rental Upgrade.com (www.carrentalupgrade.com) also lists deals. And eBay (www.ebay.com) frequently auctions off airline and car rental upgrade certificates.

Or go straight to the source: Check the Web site of the hotel, car rental firm, etc., for upgrade specials. For example, San Diego’s Loews Coronado Bay Resort (800-815-6397, www.loewshotels.com) is offering free upgrades to a marina- or pool-view room through April 4; use promo code DI1PR0.

•Stockpile loyalty points. Don’t hesitate to cash in points for an upgrade; your points have a greater value for upgrades than for securing a free flight in economy. To increase your supply, join interconnected programs; Bob Greenberg, who works at a Reston, Va., Web security company, uses points from his Marriott and Hertz rewards programs toward United Airlines upgrades.

Additionally, use credit cards with rewards programs that allow you to earn points for every dollar spent. Finally, if you have separate personal and business credit cards, link the accounts to pool the points.

•Dress well. Whether traveling by air or road, a passenger in a nice suit or neat casual wear is more likely to get upgraded than a schlep in a tattered sweater and old jeans.