Posting this link for consideration...
Mexico: ATMS and Credit Cards
https://www.tripadvisor.com/Travel-g150768-c5116/Mexico:Atms.And.Credit.Cards.html
Cards have always been the backup for me, but I know for many (or most) it is the other way around (cash being the backup to the card). Though it is abit dated now (2016) there is likely still some pertinent info.


