Upwork is far from perfect, but if you apply some rules of common sense and also have decade+ of tech experience, it can be useful.

I always allow manual time, but restrict the hours to 5 or 10 per week. If the hire does not meet my expectations, I move on and accept the lost money as a learning experience.

I don't give a negative review, I know that I won't rehire, but I don't think I know the person well enough to tell the world they are bad.

There are some great people on upwork. The best advice is to be really nice to your hires and if possible, have interesting work for them to do. Nobody wants to freelance for a jerk.