How to deter employee and customer theft?

This is we applied in US, hope that help with you in some point. Fist you should hire honest people and educate them. Pre-check employees background is an excellent way to cut down on hiring dishonest employees. You need to inform your employees about your policies and procedures related to fraud, the internal controls in place to prevent fraud, the organization's code of conduct and ethics policies, and how violations of these policies will be disciplined. Every employee should sign a form to verify receipt of this material.
In you operation, you should using a software management to track all sales and inventory, limited the blind conner by install more cameras. (Tips: for customers, you can use one and install some big and face cameras for them to see that they are being caught every singe minute in your store.)
For employee, limit access to limit theft opportunities especially in your cash drawers and the safe.
Next, You should Implement internal controls to Separate the employee duties. No employee should be responsible for both sale and receive payment a transaction. Employee has to responsible for all the goods on their sale area, pass them the responsibility to watch customers and prevent customer being theft. Perform both scheduled and unscheduled audits; investigate every incident, don’t pass any case even it’s very small. It lets employees know that fraud prevention is a high priority for the company.