I haven't been to Mexico, but I suppose stuff like that is everywhere in the world.
Recently, in Naples Italy, a friend and I were approached by someone who said they worked on one of the cruise ships. We were merely trying to find a good cigar store and were walking down an allyway.
The guy wanted to sell us two cell phones and a video recorder. He followed us down the ally until I yelled at him to leave us alone.
The worst for me was a day in Tangier. The locals there would get angry with you and call you "capitalist pigs" if you didn't buy crap from them. Later we were "robbed" by being told that our ship was cancelled to take us back to Spain. We bought another round of tickets for another ship. Then the guy asked me to give him a big tip for "helping" us out. I had smelled a rat from the beginning and refused to give him a dime. My siblings agreed to getting new tickets, so I had to go along with them.
As our "new" ship left the harbor, we saw our original ship pulling in. It hadn't been cancelled, only delayed. These guys were in "cahoots" with the security guards and everything.
Needless to say, I'll NEVER set foot in Tangier again. (But I did return home with a nice silk rug, which is in my bedroom.)