I am researching an internet based business (incorporated in USA) idea
and need some advice. Let us say, this internet based service (call it
XYZ) enables buyers seeking voiceover work to post their tasks and
registered voiceover artists (sellers) to post their bids. If the bid
is accepted by the buyer, the voiceover artist (seller of the service)
can perform the task and get paid. The business XYZ receives a
commission on each successful transaction. Now the questions:

The sellers are not employees of XYZ. However, does XYZ have to follow
any laws regarding which sellers are eligible? Does XYZ have to report
XYZ earnings to IRS? What happens if sellers of the service are
outside USA? What happens if sellers are residing in USA but are not
legally eligible to work (say, immigrants who have not received work
permission)? Is XYZ responsible to verify credentials in this case?
What else should I be aware of? Thanks.