Customer relation, a business person must understand that customer is king and should be treated like a royalty.
I beg to differ on the part I bolded as it doesn't apply to every customer. There are some customers you wish you didn't have because of their irritant behaviour. No matter how hard you try to please these ones, they won't be appeased. Perhaps, OP hasn't met such unpleasant humans. I think that expression is a cliché that rests on idealism rather than reality.
Too many customers obviously won't increase your profit, and if you're selling things at a loss to them, I don't think that's a good way to attract more customers.
Why would anyone sell below their goods at a loss and still call themselves a business person. OP didn't say sell at a loss but sell at a discount. Selling at a discount doesn't mean selling at a loss. What it simply means is that the business owner decides to lower their profit on the product.