I worked at my local Petsmart for 3 years as Petcare Lead ( like assistant department manager but not great pay LOL)
I was the Fish Nazi !!
We were taught to sell, but that the animals'/fishes' Welfare was also important !
I'm very passionate about pets. I've gone toe to toe with a customer who DEMANDED I sell her the wrong fish. I started out polite but refused to cave. She asked for a manager. He said I was the expert and my opinion counted. No Fish for her !!!
I was really into Betta and Goldfish education.
I got a family who had killed off about 3 tankfuls of fish in a row to slow down and listen and Not Give Up. They showed up a few months later all smiles and GLEE because they had 30 Cherry Barb Fry !!!
I am still learning daily. I'm 50 and got back into fish 5 years ago. I'm now a member of the oldest and largest Aquatic Plant Club in the USA. I'll be joining my local Aquarium Societies this year.
I can and do step in, but finding the right approach is key as has been mentioned. Sometimes I'm ignored. Some are rude. But I've saved Pets' lives and that makes it worthwhile.
I tell the ones who won't listen, " Please just go home and Google it if you wont believe me".
One LFS employee asked me to open a store so he could work for me LOL.
Lastly I went around to other stores and let them know that when I worked at Petsmart we sent them a ton of business. If we didn't carry something and they did I wanted to A. Help customer B. keep LFSs in business.