In such case you have to consider the situation in two ways – a theft of the goods by the purchasers and stealing of the goods by the shop employees. In both cases we recommend to install the CCTV. Even availability of the CCTV itself frightens the thieves away and reduces the personnel to discipline.
Enjoyment of the physical security is also efficient. The certified securities are trained to pay their attention to the imperceptible details and the attributes of the customer behavior showing the potential availability of some wrongful acts from their side.
To exclude or to prove such doubts in respect to the shop personnel we recommend using the polygraph (lie detector) test.