Microsoft Store

I made an appointment and went in have my computer looked at due to a buzzing noise. The store offers a free basic diagnostic and I was told that they should be able to let me know soon what work needed to be done to fix the issue. I left my computer with them and was told a few days would be needed for the diagnostic since they are quite busy. I needed to call them after 3 days. They said they would take a look that day at my computer and I was called in the next day to pick up my computer. I was told they didn't find any issues with the hard drive which was what I was most worried about. However, my motherboard was "probably failing" and I "needed" to buy a new computer. They couldn't say any specifics and said if I wanted more specifics they would need to send it to the manufacturer. When I went home and did more research I had another experienced person take a look who concluded that my fan needed replacement and the computer works fine. I felt duped that the Microsoft store told me it was just better that I buy a new computer. Were they that desperate to push new merchandise on me? Or did they not do a thorough or competent job with their diagnostics? If they couldn't find the issue, just tell me that instead of trying to push me to buy a completely new laptop!