This depends on the tax laws in the country in which you live. For example in New Zealand, if your revenue (total amount charged) per year exceeds $60,000, then you have to be GST registered. In this case, your prices are GST inclusive, you claim GST on (some) expenses, you file GST returns (2 or 6 monthly) with IRD, you advise Air BnB of your GST number in Settings.