While hosting on Withlocals you are fully in control of the expenses you budgeted for your offers. In case the guest is requesting something extra you can easily add the new costs in a personalized offer and send it to your guests to confirm and pay for. In this case there are no surprises during the experience that you are going to have together.
In case the guest is asking for extras during the experience, you should be clear about the extra costs for the additional food, drinks or an extended duration, for example. The unforeseen items need to be covered on the spot by the guest.