Paris - the "deaf-mute"children who want your signature on a "petition" - actually a phony list stating people have "contributed" Euros for "assistance" - and they will ask you to give them money too. I saw a group of them arguing (vocally!) one day by Notre Dame. Of course, when you give them money, the gush of affection and hugs will cover the lifting of your wallet - enough to leave you speechless!
More Paris - the hackneyed "Look, I found a ring!" scam already mentioned.
India - Late arrival at the airport, the taxi tells you your hotel has burned down, but he can get you a deal. Hah! And...
You take the sublevel crossing to avoid getting killed at a busy street intersection - you get your shoes and socks sprayed with ugly stuff. Of course, someone will "help" you...
Mexico - Colombian razor artists waiting for pockets or pocketbooks, especially on the metro, though it's really more robbery than a scam.
Shoe shine boys in the street who will shine your shoes - and you can see them dull within fifteen minutes, after paying a nice fee and tip for what looked like a beautiful shine.
China - "Art students" and "tea room" invitations - you find out the tea room is very, very expensive (there is very expensive tea in China, but here we're talking like a bar scheme).
Kenya - "I am a refugee from (fill in the blank with whichever country is having problems at the moment); I need your help, as I am in Kenya illegally.
I also experienced a member of our safari group who had not protected his camera gear properly and lost his telephoto lens to damage - a friendly just happened to have a lens that worked with the same SLR group. The traveler asked me to check it out - the lens was way out of collimation and did not work properly. The scammer readily admitted the fault and said "well, a guy has to try."
Anywhere - The "hot watch" scam - you can get a magnificent deal on an "Ornega" posing as a stolen Omega.
Anywhere - Street money changers - you will get anything from bills no longer in use to short-changed.
Egypt - Get taken to the "carpet schools" or the "papyrus academy".
The "friendly official" scam - for example, at the pyramids, one "official" will allow you to cross lines and take photographs from prohibited areas, another will arrive and promptly tell you you are in violation and need to pay a "fine". In the case of some friends of ours, the same official who "gave them permission" blew a whistle to call his colleague over.
The "friendly Egyptian" scam - also in other parts of the world, such as Kenya. A local asks to have a photo taken with you - and then demands money. That's not too bad, you are lucky - some people will offer to take a souvenir photo of you and your family or partner with your camera - and promptly run off with it.
London - no affiliated ad hoc "taxis" who will take you wherever you want - at outrageous prices. (This happened to mys sister had family.)
Many places - Have your guide direct you into a souvenir shop where the guide gets a handsome commission on whatever you purchase.
Many places - New Orleans and New York are famous for it - Scammers who will approach you with everything from various versions of the "shell game" to asking trick questions - "I know where you got your shoes; wanna bet a dollar? How about five?" How can you loose, right - until the scammers says "You got 'em on your feet, man!"
My favorite scam that is actually not a scam - "Genuine fake watch" sold throughout Turkey.
Telephone calls purporting to be from a friend of a relative or a relative - who has had an accident or been picked up by the authorities and needs money transferred by wire immediately. Ah, but they are merely pulling your strings, and no such incident happened - and your money is gone!
Phony gemstones - such as manufactured "Alexandrites" in Mexico and "opals" in jars of water - that will dehydrate and crack and craze if you ever try to dry them out, and many cut glass pieces, etc.
"German silver" / "Alpaca" and other nonprecious metals jewelry sold as Sterling silver, or even gold or platinum.
Several places - Phony plainclothes cops who want to see your passport - and how much money you have. Italy is good for this, but hardly alone.
Mexico - Traffic cops have a variety of cons, including if they are controlling traffic, waving you through then stopping you halfway through and accusing you of violating their instructions. $10-$20 will satisfy them.
Korea - We were approached by an "English student" who guided us, and invited us home for dinner. His "family" turned out to be five thugs who were well-armed. We handed over everything of value quickly - and returned with the police, getting it all back except the cash (no serial numbers). (We were later ordered to give everything we had stolen to the MP at the Army base we went - next day we reported it to AFOSI, and a motorcycle courier brought it back yet again.) Yes, it was a while go, but memorable.
We were "programmed" because this is such a common and innocent occurrence in Japan.
Many places - Taxi drivers who 1) have their meters running already when you get in; 2) who suddenly have non-working meters; 3) who love giving you "scenic rides" without your knowledge; 4) who short change you - the most brazen will claim you gave them the wrong, and too small, bill; 5) taxi drivers with functioning meters who set them on "multiple bags + night rates" - at mid-day.
Most people are not as friendly as they would have you believe - anyone calling out to you and asking you where you are from in a big city is usually setting you up.
Anyone asking for help at a cash machine / ATM - they are not helpless, they are setting you up, as are those willing to "help" you when you are having trouble with the local cash machine or ticket dispensing machine (except in Japan).
The ATM / cash machine scam - you insert your card, finger in your PIN code, and - the card does not come out. Often someone "helpful" tells you you must type your PIN in once again - maybe three times will do it. Nope, it won't - but as soon as you leave, they retrieve the card with the cellulose trap they have placed and - now they have your PIN.
The "shoulder surfer" - you are using your telephone card and they are watching so they can use the numbers later.
The altered cash machine / ATM - some clever thieves have placed card reader "bumps" over the card slot, and video cams in brochure holders they have placed inside the side of the niche, which record your card strip and PIN code. The most sophisticated actually use Bluetooth to send the information to someone in a nearby parked car.
In the USA - bad guys who place card readers inside petrol / gasoline pumps. Just to show how common scams are, this has happened near my home fairly recently - and many were "taken".
Not scams, but theft - Pickpockets, nearly everywhere. I have endured pickpockets as kids who rush you and hold up distracting postcards etc whilst their young colleagues try to pick you clean; mustard squirted, then people try to "help" you and pick you clean; in Lima, it's women who grab your hand to read your fortune or try to have you hold their baby - and others will pick you lean.
So many scams, and I can't even remember them all, but here are a few. Good luck with helping travelers become more aware and alert.
In Istanbul, we used an ATM; a thief reported us to their colleagues, who came around the corner and started a "flash fight", tossing one of the group at me for the "dip"; and most recently on the Athens metro, a guy stalled the people (and us) trying to board the escalator, while another went for the pockets - we bypassed them, but they got on behind us and tried yet again (a punch in the chest to #1 sent him flying into #2).
~97 countries and six decades of travel, and I have not been successfully robbed nor scammed yet. Cross fingers, touch wood, as I am off again day after tomorrow.