So, what that means is that the mechanic gets $18 per hour, times 7=$126 per day.and the business gets $117 per hour times 3 for the three hrs charged to do the job, and 7 times that for the day.
Customer brings in his new motor.
So, for installing 7 wiper motors at 1 hr each, and charging customers 3 hr labor, the mechanic gets $126 per day, and the business gets $819.
I don't like your math.
If the total cost is $45 an hour and the mechanic gets $18 an hour, the shop can't get $117 an hour. More like $27 an hour, $81 a job or $567 for the 7 jobs per day.
I don't know what it's like in FL, but in MI you get an estimate. If the final bill won't come in at the estimate the shop has to get permission from the owner for the extra cost. So the repair is a known cost and you're given a choice before leaving, pay $135 for the installation or take the work elsewhere. It's hard for me to call that robbery.