It is all about money. In Singapore when you bring your car to us for service we look at it as an opportunity to make money. The more we can tell you that is wrong with it, the more parts we can "replace" whether we do so or not, the more money we make. If you are expat we like you very much because you are very trusting and we can make more money than we would from a local who is just like us
I had the almost the same thing happen - *NOT in Singapore, and in a reputable BMW dealership.
A conventional oil service (Inspection 1) which should cost $450 - 550 generally if not covered by warrantry ... ended up being a great repair-replacement of parts (plus killer labour costs) opportunity. In the region of $2000++ too.
Ever since that visit, the coolant light on the electronic panel has always been flashing intermittently, even when it is topped up.
Fortunately for me, all replacements came with the standard 2 yr BMW warranty.
Resulting new weird noises and reactions from their 'uncalled for additions' were looked at free of charge. But NOT so when they determined again any fault wasn't from their repairs. Worse is when probelms cannot be diagnosed at all.

Ongoing saga.
At the end of the day, it's like going to a doctor when going to ANY mechanic
(NOT just in Singapore imo).
Happens when you really don't know that much about what is what, and what really needs to be replaced.
Opening a whole can of worms.
It could be something as something as a cut on the knee needing a mere band-aid being blown up to 'needing stitches' or even escalated to needing surgery' proportions. Be it doctors, or mechanics - go for a second/third opinion.
Integrity? What is that?!