Indeed! The Service Engineer bears the brunt of customers' problems and complaints. He invariably gets called in when things have gone wrong, and gets to meet people who are rarely (if ever) seen by the salesman. Oh, what a joy!
But let's be clear about the distinction between the Service Engineer and the
Sales Engineer, who are (I believe) usually on commission, just like sales staff.
And ... going back to what our friend in Turkey is saying:- I reckon that the Service Engineer (and I'm really talking about the biomed variety) is motivated by things other than money anyway.
To put it bluntly, sales people (like managers) are "two a penny". You see them come, and you see them go. In my experience I was always happy to wave them off to greener (that is, by their reckoning at least, more lucrative) pastures.
But don't get me wrong,
someone has to be doing the selling (on the
Dark Side - that is, in the private sector - at least). No sales means no revenue, which means no new test kit ... and worst yet, no salary for the Service Engineer!

But selling
service (maintenance) is not the same as selling "boxes". What customers really want is an efficient service, and quick (that is, as quick as possible) turn around time. They also prefer the job to be done right first time! They don't really care too much about the details (no
hard sell required), but just want their kit back, working properly, ASAP.
Yes, Sales and Service is the tradition business model with medical equipment (just as it is with cars and trucks), but personally I prefer the ISO (independent service organisation) model. That is, service only. Potentially less profitable, but a more honest way of earning a crust, in my opinion (and, need I say it, no conflicts of interest).
