Imagine you went into a shop and spent a lot of money buying something you later discovered was an expensive mistake. How would you feel about the sales person who sold it to you? What if the sales person just gave you what you asked for without checking?
I was having this conversation with a client today whose opinion was that every sale was a good sale. Is it not the buyers problem if they had specifically asked for the wrong product?
It seems counter intuitive to question a buyer who seems to know what they want. Would you trust a sales person in the future who just stood by and watched you make an expensive buying mistake? Conversely you are likely to listen to a sales person even more if you had ignored their previous advice to your regret.
If you want to get to become a trusted advisor to your clients, and benefit from all the sales advantages that come with it, then you need to be prepared to advise!