I think you probably want to tell them to go somewhere larger then like Cancun or Puerto Vallarta... a city that isn't too huge (crime rate is lower then) that still has tourists, because it means there are better ammenities.
They might really like a village like Sayulita. There are still roads and cars, running water and toilets, warm showers, and it's a nice young crowd. It's located north of Puerto Vallarta.
Have they ever lived anywhere like Mexico? If they haven't at least spent a good three or four weeks there, they will hopefully consider a long vacation first and then decide if they really want to buy. Living there is a LOT harder than just spending a week there on holiday. When I moved there, it took months just to get my phone line put in. Having an appointment somewhere doesn't really mean you'll get in that day to see anyone. Electronics oddly stop working for no reason at all (probably humidity problems). Bugs are really big. Water stops flowing. Power goes out. And getting an FM3 to live there can be a huge run around.
Just some thoughts, just in case they are newer to this.
