Given the inherent risks of a virtual or remote employment scheme, it's pretty much standard practice to try someone out via contract work, then if they produce good results to offer them ongoing work – either part time, which allows them to continue contracting, or full time.
In the case of "buying out" an online contractor from somewhere like oDesk.com, freelancer.com, etc, the worker agrees to terminate their account when signing the employment agreement.
It's actually fairly common – if you can find someone who does decent work on time consistently for a fraction of the cost of a local worker, it makes great sense to both give THEM steady reliable work, as well as lock them down enough to make sure you're their only pending deadline.
What are the best resources for finding remote or virtual jobs?
deano.com 