@Ginny40
Hi Ginny, you can offer anything you like in your listing description! There may not be an applicable charging mechanism within the Airbnb booking program but, you can request whatever you charge through the resolution centre and, if the guest approves the charge it just happens....you will be paid!
My only word of caution would be, make sure your public liability insurance coverage will cover your specific situation!!! Many....or should I say MOST insurance companies will cover liability claims that arise from ' accidents' on their insured property but, a horse riding experience you are promoting can be seen as a part of a commercial contact being part of the hosting agreement and would fall under the same category as a bicycle hire company and require commercial insurance coverage, not domestic in the event of a claim! You will be covered for family and friends, but not paying guests!
Good idea Ginny, but just make sure of your insurance coverage.
Cheers.....Rob