Pet shop worker lied.

Went to get some fish at the pet shop, half the fish in the tanks were dead. (Red flag 1). I told the worker about it and she simply didn't care to remove the fish, dead fish spike ammonia (Red flag 2). She told me that small tiger bay fish were not aggressive so I got 6, she also told me that they were okay with snails (Red flag 3). Once I got home they acclimated fine, I monitored the fish and they all seemed to be fine. The next morning I woke up to only 1 fish in the tank and only 2 snails. They must have started fighting and ate eachother. What can I do about this?