Yes, this is not the best idea. Are you considering a month to month lease, or a year's lease? A large % of small business startups are not still in business five years later. It has been estimated that half of small business startups are not still in business two years later. How much experience do they have with what business product the business will be offering/selling? Have either one of them run their own business in the past? All of the income that the rent will be based on derived from the same business does not always weather the lean months.