1000% you need a minimum.
How you figure this out is really understanding your numbers. For us, we used to do a 1/4 day min charge. What I found out is people were trying to run my guys around to get as much out of us as they can. I would net less than $100 of profit on those jobs then we would have call backs because my guys were rushed then poof there goes the profits. Then we raised our min to a half day - $500. You know what? People still tried to run us around but at least my guys had the time to actually repair the issues. People complain it's expensive ... so is my cost of doing business! One thing I started doing is I found a comparable business with a lower minimum that would be ok with lower value you jobs. So we send them referrals and they pay us a fee for it. Boom problem solved.
