It is a common practice for service companies like hotels, resorts and restaurants to be providing WiFi Internet access to its customers. However, there is a common mistake also for such companies. The WiFi network is on the same network segment as the office computers. This is a security issue because now you are allowing strangers to have local network access to your computers.
In order to avoid the issue where the WiFi users can access your local network, the office network must be on a separate network segment, with its own router and firewall blocking any unauthorized access from outside the network.
Another concern with sharing Internet access to customers is that your own Internet access might become slower also because of the increased download and upload activity.
There are firewall devices available on the market that allows you to segment the network into two or more subnets. You can put the office network on one subnet and the customer WiFi access on the other. Then on the firewall, define the rules such that incoming traffic from the customer subnet is blocked if it is going to the office subnetwork.
With a little change on the network configuration, one can increase the computer network significantly. With the constant threat of malicious Internet activity, it is important for business owners to secure their computer network to protect its business interests.