The check engine light turned on in my Volvo XC90 ...

The check engine light turned on in my Volvo XC90 and I decided to take it into a volvo dealership to get proper service. That was a mistake. They did a compression test and Rodger told me that the only possible solution was to replace the whole engine, quoting me something like $9,000. Rodger said the cylinders were broken and a rod could explode through the hood of my car. When I asked what was the specific cause of the low compression numbers they said that they did not actually spend the time to diagnose which parts were causing the low numbers. They said they were saving me "time/money" by telling me to replace the whole engine. Then they refused to change my brake pads because they said it wasn't worth it unless I replaced the engine. Then the next day the check engine light wasn't on anymore and I ended up driving the car 300+ miles with no issues, took the car into a different mechanic. Got the spark plugs replaced and a few other things for +/- 500$. The car still hasn't exploded 7k miles later.