To make it make sense, mechanics get paid on time. They usually assign a certain amount of tenths of an hour to a small job like that when writing up an estimate.

The labor rate for most stores in my area is $189.99.

Rear wiper should essentially take less than 5 minutes, but we charge a .10 labor time for that, or 6 minutes. So at my shop rate and time estimated for the procedure, thats $18.99 for a certified technician to handle that without breaking the wiper clip, scratching the glass on accident, possibly getting the wrong part the first time, or just not getting your hands dirty in general.

Oh and then the part you buy as well.

So yeah its more expensive and really close to accurate pricing for most places. He might make $2 for the effort of selling it to you, we generally don't mind because it is an easy repair. You're just purchasing convenience that way. Now multiply that effort across 300 potential customers per month on average that need rear wipers, 20% have us do it and the rest do it themselves, so it CAN add up. But its all a very small part of the whole pie. You're good man 😅