Can I save you a bunch of time? Direct him to the dealer, go ahead and be cordial, etc... But don't get too excited about caches in Mexico. There is so much ingrained superstition about caches in Mexico, that it seems every immigrant who moves here, is simply convinced that caches exist in every cave and backyard "back where they're from"
Where I'm at in CA, we have a lot of immigrants d/t the agriculture work. I have run into countless of them, who, like you experienced, come up with fantastic tales of buried treasures, that "if only they had a metal detector back in their hometown, they'd be rich!" But when you press them for details, it's always someone who told someone who told someone, etc...
Back in the mid 1990s, I took the plunge and accompanied an employee of mine back to his hometown high in the Sierra Madres to detect for "several caches he was sure we could find that he knew of". We got there and searched ruins and old homes dirt floors till we were blue in the face. Got some fun stuff on a coin-shooting level (old relicks, etc..) but no caches. As we began to get discouraged, I decided to pry a little more about the nature of these cache leads he had brought me down there to search for. It turns out that stories that ...... back in the United States ... sounded so fool-proof-certain ("first hand and indisputable") were now crumbling. Like "gold coins that he had seen" turned out to be "Well.... I didn't actually
see them, but I heard about them from a friend... blah blah blah" One by one I began to see that all his cache stories were well-intentioned, but merely passed-down stories and superstitions.
After a week in this little high-mountain village, as word spread that "americans were here with metal detectors", other locales began to ask us to search their backyards, or a cave or a ruin or whatever that they knew about. In each case, they were certain we'd find a treasure there. After many un-succesful hunts like this, I began to ask our hosts "how do you
KNOW there's a treasure there?" The answers were somewhat comical, but they were insulted if you did not believe them. Things like "because I saw smoke coming from there" or "because I saw a glitter in the soil" or "the virgin mary told me in a dream" etc... etc.... After awhile, we began to turn down all such requests to chase these stories. It had to be first-hand (not someone who told someone who told someone).
No matter how much I stress this, believe me, the stories will be compelling. But if you really press them, very few are credible or firsthand. Not saying there's not caches down there (and up here too for that matter). Just saying you've got to enter in the superstition factor of the culture.
My only suggestion to anyone going down there to cache hunt, is to use a 2-box unit that will not find anything smaller than a soda can. We took standard detectors thinking "no problem we'll just mentally ignore any small signals". But it's nearly impossible to do, as you spend all your time trying to differentiate an endless stream of signals all blended together. A 2-box unit makes that nice and simple because you merely don't hear the small things
The trash is simply unbelievable down there! Only the biggest cities have curbside trash service. So unlike here, where you put your trash out on the curb to be taken away, down there, in little villages/towns, they burn it, bury it in their backyard, or just take it out to the country or the nearest gullies and just dump it. We found trash, even modern trash, at the most remote of ruins.