There are reasons why one is supposed to get a license to do work like plumbing. When those reasons are applied fairly, it benefits everyone.

I almost bet that, if Joe cann't 'yet' pass the exam, there are jobs he is not able to do in plumbing...but if he takes a job and hits an area beyond his expertise, the temptation is to fake it & hope, rather than farm out the job and lose money.

   *I* can fix a leaky faucet or clean a drain or run a line for water to a refrigerator, but I sure can't install sump pumps or do copper fittings....etc.

Joe needs that official license.