Any time the consumer feels his rights have been violated and the other party is not cooperative (the defected good is not accepted for service and repair during the warranty period, the specification of the product differs from the ones advertised, etc.). However, it is important to emphasize that such harms have to be proved. Make sure there are written proof, for example signing the book of complaint, keeping an issue of the concerning advertisement, etc.
In such cases, do not hesitate to turn to the authorities!