Well, in every shop there is a donation brick. This is used so players can donate to the business owner and then the owner will provide the services. Another business won't buy the services, an individual customer will. If the customer refuses to pay or does not pay after the services are complete, the customer won't receive the product.
For example, if you were selling building services or furniture, you would allow customers to donate a fixed amount to the company and then you would provide the service. You can't take their money and run because you will be punished.
There is a relay set to every business owner that gives them tax and income at fixed intervals, also.