There is grey in what would be considered their work, so 100% guarantee is not specific enough. Typical payment is a third up front, a third half way through, and the balance upon completion. Handymen are fine for some types of work, you want licensed insured trade people when you get into large, more complex type of jobs.
poor quality work or have a bad work ethic, are also subjective terms. Then you also get into the grey areas where it may appear that a trades person is slacking. Such as bleeding a hot water system. But basically that is standing around waiting and watching.