You should only post your question in one section, TNJ
Pesos are the legal currency here. I have seen instances, in supermarket, for example, where people have paid in dollars. But this caused delays as cashier had to call a manager who had to figure out what exchange rate to allow and how much change customer was entitled to.
When you pay in dollars, you are stuck with whatever exchange rate the person receiving the dollars decides on. There is nothing hard and fast that requires all to use same exchange rate.
Whether to exchange there or here, depends in large part on what rate you can get there. Exchanging here, do not exchange in your hotel. they customarily give a lower rate.
You might indicate where you will be going for your visit. Someone familiar with that area can make suggestions as to best place(s) to exchange your dollars for pesos.