He also warns that one must keep the dollars undamaged and in perfect condition. They even recommend to notify the banker on duty at home so that we can exchange the euros for dollars that are in good condition. Apparently, to the minimum breakage or damage in Peru they do not change them or by hint. Although I would like to see it in person ...
On the other hand, the falsification of both suns and dollars seems to be a common practice in Peru -And in which country it is not ?, I ask myself- ... The guide advises to observe the bills checking the watermarks against the light to see if the colors change and if the texture of the bill is rough and with fiber.
As for ATMs and credit cards, both VISA and MasterCard are accepted in most places except for remote areas. The commission for purchases is usually between 8 and 10% so it will be worthwhile to take money from the ATMs and pay in cash. There are ATMs that charge a commission dollar for making any transaction, make sure that the cashier you use does not follow this practice.
I suppose I will do the same as in Southeast Asia: a loincloth with a wad of suns that I will take out at the first ATM in Lima I find and a few dollars in 10-dollar bills in case they are needed.
Guides tend to be extremely cautious, but you should never underestimate this kind of advice. If we have any Peruvians among the readers, it would be good if you would comment on this.