Went and bought a camera charger and battery to fi...

Went and bought a camera charger and battery to fit an old camera. One of the workers opened the battery to see if it fit my camera (which it did) and once I got home I decided to return everything since the camera was too old. When I went to return said battery and charger, they wouldn t let me return the battery because the packaging was opened but I wasn t the one that opened it, the associate did. Why would I not get my money back if I wasn t the one who didn t open it in the first place?