"Satisfaction guaranteed," is quite frankly a super doper crappy guarantee. It will take a lot more than that to stand out from the crowd. Try some thing like "We are so confident that you will be 100% satisfied. If you aren't, then in addition to canceling your fee we will also insist on paying for another lawn care company to mow your lawn."
Now imagine if you saw two adverts in the yellow pages. One with the first guarantee and one with the second. Who would you be more likely to call? that’s right the second one obviously!
Don't worry about people ripping you of. It almost never happens and if it does, then don't sweat it. It's no big deal really.