Allow your customers to book tours now and ahead of time by offering live availability.
By not offering live availability you open yourself up to double booking and cancellations. This will not only annoy your customers, but damage your brands reputation.
Offer a real-time calendar as part of your booking process as this also caters for impulse buys.
There is nothing worse for a customer than to make an enquiry to only be told it is not available. Chances are they will go elsewhere.
If they know dates upfront, they are more likely to change their plans to suit your availability than change this over a phone or email conversation.
Filming location: The Ark Houseboat, York