I would not be asking around for a pound if I were you in that case. I mean, what, are you going on vaca for a YEAR or something?
:wtf:

I smell fish... oh wait... that was the fish n chips I had for lunch... no really... something still isn't right here.

I've never been to Mexico but I CAN say, treat it as you would any area where you aren't that familiar. Stick to the heavily populated tourist districts, don't go alone with anyone, and for the love of Pete, don't be asking for no stinkin' POUND of anything!!! You might as well say, "Hello, my name is Tourist with cash in my pocket, please hassle me/ rip me off/ arrest me/rob me."

This thread is kinda borderline too BTW.
I'm responding and leaving it up because I think you are about to put yourself in a risky situation.
So PLEASE PLEASE PLEASE be careful.