Aaron, here's my tip. When you are new, practically every invitation you get will be from a scammer. I didn't start getting "real" invitations until I had started getting some traction on the platform. Invitations are always exciting to get when you're new but they aren't real jobs.
Who knows how that client got good ratings? Did he post real jobs and get real feedback? Or did he have friends take on small jobs and pay them to give good reviews and then have them pay him back the rest. All against Upwork TOC, but scammers gonna scam. What you probably realized, is that unless there is a contract in place the freelancer can't leave any feedback for the client. So no matter how many times the client has done this and gotten free work, it isn't going to affec his rating. Just be careful and don't do any work until you have a contract in place. And before that, really juts rely on your gut as to whether the job sounds fishy or too good to be true. I think that I have maybe gotten one scam offer/invite here. Bump up your hourly rate. You can always bid less on a job, but a higher hourly rate does tend to scare off scammers.