Buying isn't Selling. A clients walks in to your business, asks for X and you give it them. Have you sold anything?
Selling can be defined as 'exchange for money: to exchange a product or service for money, or be exchanged for money' - so technically, yes you did 'sell' something. But they bought something which they convinced themselves they need or want - you just happened to have what they wanted.
Continuing this story - this customer then complains - they come back to you and say 'you sold me this product/service, and it doesn't....'. True! You created this problem by focusing on the 'sale' - not what the client really needed by determining what problem they were looking to solve or opportunity to capture.
Selling is defined above - but it is what happens before this exchange which creates a relationship - and from a relationship regular 'sales' can happen, sometimes no 'sale' as it's not in their best interest, maybe a different 'sale' and, even better, sometimes your client will 'sell' for you if you do it properly.
Don't focus on the sale - focus on the journey to this point.