re: "In the past I have seen some jobs where you have to pay for a background check."
Lars, thank you for your comment.
But this actually is not true.
In the past you saw SCAMS that were posing as jobs where you have to pay for a background check.
A real job does not require a contractor or employee to pay for a background check.
Lars, yes, they are all scams.
If you see a job posting on Upwork that requires you to pay for a background check, or... if during the interview process the "client" mentions that you will be asked to pay for a background check... then it is a scam.
You will pay for the background check. The "client" will pocket your money. You (might) be assigned some work to do. You will never be paid for any work.
It is that simple.