Will I need cash on the day?

Sometimes, and the tour page tells you before you book. Most tours are paid in full by card when you book; some guides take a small deposit here and the rest in person on the day.

When that is how a tour works, the price breakdown says so and names the amount you will still owe. It also says whether the guide can take a card; if they cannot, bring that amount in cash.

You see the amount again at checkout, in your confirmation email, in the reminder the evening before, and on your ticket. The total is the same either way, and nothing is added for paying part of it in person.