Please feel free to drop your own ideas on how to increase profit in businesses.
customer is king and should be treated like a royalty.
Not always. There are some "toxic" customers and time-wasters who come to your shop without intention to buy anything. You will lose your time and efforts to sell but the deal is impossible as they were not even considering buying anything initially.
Stock different brands of the products that you sell.
Sometimes this works against you too. If you sell items of one or few specific brands, you have your own loyal customers, easier to control stock, do accounting, buy items etc. This saves a vast amount of time and work. The more time and energy you have, the more you can achieve.
Think about it.