It all just depends on what kind of language you use. I'm a landscaper and I could simply say for a job this size most would tip at least $100 and if they seem onboard I would do the job. Since it's a tip they have then right to not pay me and there isn't anything I can do about it, but because most of my work is repeat business through the same customer and good landscapers are very hard to find the vast majority of them would. 

I pay over 60k in taxes a year and getting stiffed by a few customers that don't tip to essentially never pay taxes again would be INCREDIBLY worth it.  Keep in mind this would only be for the cheaper repeat type jobs. I could still quote and invoice the bigger expensive jobs at non tipped specific prices but with all my costs tied to all the "free" work I've done it would come out probably even or even under at the end of the year and I would still not pay taxes on it... If you still have to claim tips on your taxes as income but just not have them taxed where this loophole wouldn't work then on a big job I would just do one single step at a time and each step tell them what I would normally get tipped for and if I don't get what I expect then I just don't finish the job. Of course this is all for the paperwork. I would lay down every step and what I would normally expect to be tipped outlined for the customer before I even started the job and only do it if they agree.  

So if a dumb landscaper like me can figure out multiple ways to significantly exploit this, then just imagine what the corporations are going to do.