responsible traveller
Remember that if you work with people who don't have a legitimate business you also work with people who don't pay taxes and thus steal from the society they are living in. This is why they can be cheaper than honest businesses that act correctly. As a responsible traveller, it is your duty to pay taxes where due. As a responsible traveller of course you choose to pay your taxes where due in the country you visit. You only work with people who will give you a legal invoice in Peru that is either a "boleto" or a "factura" with the name of the business and their VAT number printed on it, together with a unique number.
unesina
There is a website of the "Union de Negociantes sinceros de Nazca" (http://unesina.org) meaning the union of honest businesses in Nazca that tells you where you should and shouldn't do business. They base their content on interviews with tourists while they are waiting to travel out of Nazca to their next destination.