Creating a marketplace for tour activities
As someone else suggested: take a look at the Booking and Availability Management Tools for Drupal (BAT). 

Roomify.us, the business providing the BAT framework announced that they are also providing solutions specifically for tours and activities rather than just rooms and fixed places.

The BAT system integrates with Drupal Commerce and its various payment gateways. It also takes over the Drupal logic very well with 'types', 'type bundles', 'events' and 'units'.

Once you understand how it works conceptually it should not be too difficult to modify BAT so that it can become a kind of marketplace where users can create their own units on the basis of pregiven tour types you have defined.