As they aren't gov regulated, I would check what the rate is before doing any transactions. I asked some of my 'friendly' motoconcho guys where the best one is and they told me, they always know the best one locally. I have been going to the same place now for a few years and he does me a good deal, which is a bonus! You should be able to change pesos to dollars and vice versa at any of these places (as well as most banks - but as dv8 says, you will need ID at the bank) and I know a few banks here in PC that won't change money unless you have an account with them.