newkidontheblock, you mislead people. no one agency wouldn't issue a Visit (tourist) visa for someone who they want to hire. This is illegal activity, why to take this risk? Your friend most likely came to qatar on Business visa, which are issued for the short term employees, and which is perfectly legal.
You can work only having following documents:
1 Work visa (under company or private employer sponsorship)
2. Work permit (while you are ander your family member's sponsorship)
3. Business visa (for short term employees)
Any other types of visa (family, tourist, on arrival, etc.) are not allowing to the person to work in Qatar.