MeFite spikeleemajortomdickandharryconnickjrmints talks about what sort of routine maintenance your bicycle is likely to need.
the big takeaway is that you need to ask your shop to break down the individual items on the estimate and also tell you WHY things need to be done. We expect to get called out on every recommendation, so we don't just make shit up, ever. If we say your wheels need to be replaced because your braking surface is worn, then we will also be ready to break out the tool that indicates this. If your shop says something like that, by all means reply with "Ok, could you please show me why you think that needs to be done" and if they wave their hands in the air and give you woo woo or something, fuck 'em.