What i have learnt from standalone store owners

This is the duration of some of my relationships: 

Grocery store - 18 years 

Stationery Store - 18 years 

Electricals - 18 years 

Fruit vendor - 7 years 

Dry Ration - 2 years 

Cleaning supplies - 8 years 

Medical store - 6 years 

Florists - 7-8 years 

And over these years, I have learnt a few things from these wonderful people. Here are some of them: 

A. A simple board outside the store asking what they can stock. No AI needed to do inventory management and get new product ideas. 

B. Personally greet every person walking into the store. At one store, every customer gets personal attention and its a pleasure to go in there, even for a small thing. 

C. Be realistic about setting expectations. Tell them when something will be available. 

D. To the customer, you are the subject matter expert. Play that role. 

E. When a better product or offer is available, give it to the customer proactively. 

F. Indifference is the fastest way to lose a customer. A positive interaction goes a long way in retaining a customer.

What are some lessons that you have learnt from your interactions?