Only reason not to let you in the shop area is necause of liabiility insurance, but since you are in Mexico I'm not sure about that. Any shop that doesn't let me see MY stuff won't get my business. period.
As for changing the tire yourself, watching someone do it once is the best way to learn the basics. Not hard, but knowing techniques will help a lot. http://www.youtube.com/watch?v=QQDW_jk_zdM
As for changing the tire yourself, watching someone do it once is the best way to learn the basics. Not hard, but knowing techniques will help a lot. http://www.youtube.com/watch?v=QQDW_jk_zdM