I dunno, do you tip the illegal immigrant who mows your lawn??
I have a maid service that comes to my home once a week. I always request the same person. For 2 1/2 hours of work, the company charged 86.00. I always pay cash and give 100.00. She goes about what they say they do. On their website, they said up front, they do not do laundry, or dishes. They do not move heavy objects (dog cages in my case). She does my laundry, all dishes, and will move and mop behind and under all my dog crates. Just this pass week, I was sick. She spent an extra 60 minutes at my house free of charge to finish cleaning up the extra mess I left laying around. If for some reason they have to send someone else out, I wait till I see the work they do before deciding to tip them. Even when money is tight, shes understands and does just as good of a job that she normally would do.
Ugh... gentlemen on a style forum suggesting that you not tip a professional service...???
How banal and how pedestrian.
Of course, you tip, old sport.
And even when the service is sub-par... you just tip less.
If it is an infrequent maid, mower, private car-type service (ie., more than a month goes by between uses) then you should generally tip 15-20% of the bill after each visit.
If it is a frequent professional service visit, then you can opt to tip each time, ask the company to add a gratuity to the bill, or give a seasonal one-lump-sum "gift".
So, please uphold the "style" standard for which we all endeavor, and keep this simple rule in mind concerning tipping: if you can't afford the tip, then you can't afford the service.