First of all, you need to verify as a provider of such vouchers, if you are contracting with the consumer only for the voucher or could the consumer consider you to be an agent of this hotel or all the hotels and therefore, place you in direct harm if anything should go wrong (from as simple as a lost reservation to injuries on the premises). Every state is different and some do require you to not only be registered with the Secretary of State in that state to do business with those state's consumers but you may need additional licensure as a travel agent. Some states don't require such licensure for travel agents. Some states have a registration system for such work. Check into any insurance you may need or would be helpful to have and consider at least consulting with a business attorney about setting up your business to protect you from personal liability and of course to help write the disclaimers needed and contracts needed for your business.