Possibly not for either of your accusations.
Usually fish die in the first few hours due to shock. A way to prevent deaths in the future:
*Whether you have just set up your new tank or not, this should not kill your fish.
1. Check your PH before adding in the fish. Adjust your PH accordingly and as close as possible to 7.0 as you can.
2. You will need water ager to reduce the chlorine in your water, you need to do this every time you fill up your tank or replace the water entirely.
3. Make sure that your water is at about 22-28 degrees.
4. When you have bought your new fish, keep them in the bag that they came in and put the entire bag in the tank, leaving the elastic band on the bag.
5. When you are doing this, turn off your light to reduce shock. Natural light only.
6. Leave for about 30 minutes to an hour.
7. Release the elastic and let the fish swim out of the bag on their own.
8. Do not remove the bag out of the water until all fish have left the bag on their own.
9. Feed the fish.
10. Wait a few hours until you turn your tank light back on.
Good luck.
Answer to your additional details.
No, companies don't want you to take the dead fish in, ha ha.
However, with that being said, they can give you replacement fish if you tell them your situation.
I bought two angels, five guppies and a cat fish. All but one lived, an angel and my other angel got pretty upset after that. I told my local pet store what had happened and they told me they could replace him/her, but I disagreed because I don't believe in just replacing a pet.