Struggling with bad hires as a client (lower availability than promised to be the biggest problem)

I have been having really bad luck hiring freelancers on Upwork. I always hire on an hourly basis to be fair to everyone.

Most of them over-promise and under-deliver.

My biggest pain point is that freelancers lie about their availability all the time.

Before hiring, they promise to work 4-6 hours/day. They do it for a few days after getting hired. Then it reduces it to barely 1-2 hours/day.

If I try to end the contract, they start begging me to give them another chance.

Usually, those freelancers have access to very sensitive information as part of the job, so I don't want to have a bad relationship with those freelancers worrying about retaliation.

So I usually give them another chance. And then months are wasted like this.

Skill is another problem. However, I am able to find better freelancers by asking them to work on screening tests.

But I have no idea how to find freelancers who work promised hours?

Any suggestions?