I am a ("Top Rated") and 5* freelancer on Upwork, with a 100% rating for completed projects. I refuse any / all offers from Upwork clients who even hint @ inappropriately working outside the network, but I do report them.
Neither do I accept offers without a subsequent interview of the client so that I can be confident that we are a good fit. I occasionally do suggest that I submit a "free sample" or a preliminary draft prior to executing a contract. I simply have enough confidence in my work product to provide protection the client.
More importantly, I can also protect myself and maintain a sterling reputation for not only quality, but integrity as well. In the previous 12 months, I have invested less than 2 hours into projects that didn't come to fruit, while saving 100's of hours in unnecessary revisions or interim consultations.
The approach also allows me to avoid unreasonable, unqualified clients with whom collaborations become difficult or may have given me less than stellar feedback ... who originally felt the need to hire a writer and then become "experts" on the art and science, retroactively.