This I agree with. While the local pet store was in error what the heck their sloppy work. It was the OP's responsibility to vette the store, find out how much experience and success they have had.
It is a shared responsibility.
I just had a heat wave disaster when one of my temperate tanks chiller blew a fuse in the middle of the night. When I woke up, the tank went from 64 deg to above 80 in a matter of hours. lost two sculpins, some urchins, a load of mini brittles. Is it my fault that the chiller blew a fuse? No. Could I have done something to prevent all of this? Yes. I could’ve easily installed some sort of temp alarm.
So ultimately what had happened IS my fault.
Now your going to extremes... but yes, you put your grandma in a fly by night nursing home... Yes that would be your fault.
And now your being mellow dramatic... You are good with the words, but it's your actions in life that counts.
@jmichaelh7 was being supportive. He was trying to give you a valuable lesson in life.
You can collect that participation trophy in life, or you can bleed a bit, cry a little, learn from your mistakes and get the trophy for the win.