I've often wondered if there isn't already something in place to try to prevent specific, known individuals from buying a ferry ticket.
I can't imagine what that would be unless you think Mexico secretly has some super high-tech surveillance system deployed. Most tickets are bought in a 30 second cash transaction with no id shown or signature required. The tickets are taken by hand and barely looked at as you board. No disrespect intended but this is a country where you are delighted if the shower has hot water and the internet works well enough to use FB.