You're correct about toxic customers who just walk into a shop without any intention of buying anything. I personally treat all my customers with utmost respect, because there's no way of knowing a serious customer unless when you're attending to them. But if I'm convinced that they've come to make trouble, I'll politely ask such a person to leave my shop.
For business people in general, they must treat their customers in a very polite and courteous manner so that customers have an attraction with the services we provide for them. After all, whether a customer is serious or not when shopping is when he starts asking questions and tries to respond to the service we provide for him, so the main thing is to keep serving before we invite him to leave after knowing that he is just playing around to make trouble.
Stocking specific brands works for big business people, but small business people like me sells more when we stock different varieties of brands that customers can choose from.
I think you have also implemented a very appropriate strategy in this regard because for small businesses it is better to provide more brands as choices for customers. Because we also don't know what brand a customer is looking for, so providing more brands that are well-known and widely chosen by customers in general is a pretty good strategy to attract more customers to our store.