If you hand out gifts to a group, make it clear in advance that you intend for them to be shared.
Some aid organizations say it's just as harmful to give trinkets as it is to give money. "A gift that can be seen and touched," says Terri Speirs, who organizes tours of developing countries for Lutheran World Relief, "has the potential to cause unintended consequences by introducing dissent and jealousy, changing an equal relationship to one of have and have-not and reinforcing the one-dimensional image of rich Americans. It can make the next group of visitors easy targets and even create a security risk." In my experience, however, offering children small, inexpensive items in a way that engages them in a shared learning opportunity—say, giving them postcards from where I live so they can learn about my country as I learn about theirs, or carrying a Polaroid camera and leaving them with photos of themselves—has often been warmly received and has led to many a mutually gratifying exchange. If you do opt to leave gifts, though, "make your intentions clear at the start," advises Callahan. "If you're taking a photo of a group and you mean for the group to share it, make that clear before you snap the picture. If you give a pen to one child, there may be a hundred more who need pens, so make it clear in advance that they have to share." Better yet, if you brought along a package of pens, take it to the local school and give it to the teacher, who can distribute them fairly.

If you pay in exchange for a service, make it a small amount.
Say you want to give to street musicians playing at a monument. Contribute the same amount the locals are giving (the equivalent of one dollar is often far too much). Otherwise, you risk reinforcing the belief that Americans throw money around, says Lewis.

Don't be pestered into purchasing a service you don't want.
When I was in Vietnam, several people pressed relentlessly to shine my shoes even though I was wearing sneakers. Similarly, if you're stuck in traffic in some countries, people will wipe your windshield with a newspaper (which only makes it dirtier) and expect you to pay. How should you respond? Just say no—politely, firmly, and, if necessary, repeatedly. What if someone "washes" your windshield even after you've asked them again and again not to? "Don't reward people for treating you badly," says George. "That's a hard thing for Americans to remember because we have this sense of guilt and privilege and we worry about being polite and not offending people." Some locals read politeness as uncertainty, Lewis says, so be very firm.

Learn a phrase that means a forceful no.
Ask the tourist office, or your hotel's desk clerk or concierge, for a sentence you can use when someone won't stop hounding you. In Egypt I was advised to say Eeb! which means "Shame on you!" in Arabic. In Jamaica, Lewis extricated herself from a common local scam with "You know what? I'm not a tourist. I live here."

Contribute to a local aid agency.
Make a donation to an NGO that helps the poor at your destination. Instead of shopping for souvenirs in state-run stores, find out where you can buy products made by locals. In Siem Reap, Cambodia, I shopped at Les Artisans d'Angkor, a studio where the rural jobless are trained in the ancient art of Cambodian stone and wood carving. In Phnom Penh, I bought silk handicrafts made by the disabled at the Maryknoll Wat Than Center.

If you promise to send assistance later, do so.
Don't write down someone's address and say you're going to send money or supplies if there's a chance you might not follow through. "All it takes is one broken promise to crush the goodwill that has been built up by other people over the years," says George. "Each and every one of us is an ambassador."