Mystery Shopping?

Is it good for business?

Mystery shopping could be:
1. company using a mystery shopper to check on itself - how well it answers the telephone, how politely and efficiently it deals with a customer's request, how stock is presented ....basically about the customer experience and how it can be improved. The more companies that do it, the better should be the customer experience throughout the industry but I think you'd need to consider whether it was boosting total business or just moving business around between companies.
2. company using a mystery shopper to check on its competitors - not exactly industrial espionage but more looking for how the competitor achieves its competitive edge so the ideas can be copied or bettered;
3. regulatory body or trade association using a mystery shopper to check that a company or service or utility is complying with relevant laws, regulations or codes of practice.

Is it good for business?
Example 1 is good for the business in question if it gains valuable insights into the customer experience and acts on them. What is good for the business that improves itself is not necessarily good for its competitors.
Example 2 may be good for the business that checks on its competitors and finds a way to improve its own customer experience or competitive edge. Obviously, it dilutes the benefit to the company that came up with the idea originally but you can't stop people copying your good ideas (unless those ideas are legally protected, though I don't think that is relevant here).
Example 3 is beneficial to the industry as a whole because it makes it harder for one business to save money by shirking its obligations and is beneficial for each business checked because it lets them know the strengths and weaknesses of their own compliance programme. It also boosts customer confidence for the whole industry.

There is more work to do so you really need to think about the background to the question and what you are being asked to demonstrate. The question as posed is too simplistic to be answered properly so it will be up to you to pull it apart and knock it into shape. With luck, I have given you some pointers.

I think it is. My husband works for Lowe's and he actually got a bonus because their mystery shopper gave them a gold rating. I also think it's good to see how your employees are treating the customers when they think no one is looking.

Sure.
It lets one business, like a store, keep up with how a competitor stocks his store, and their pricing on particular items.

Yes, it's a great source of valuable information