yes the black market will be larger but not to large their are natural limits for how much a business can spend under the counter. so it`ll never be at a serious blatant level. notice all thoses nanny scandals from politicians.
There are also natural limits to how much the government can declare value by fiat.
When the government approaches these limits , it destroys jobs and potential jobs.
Some of these jobs move to other jurisdictions , some of them become black market jobs, and some of the jobs are just gone.
How many people are pumping gas for the customer now?
The demand for full service gas stations never was lessened , but the value was less than could support the higher minimum wage.
Since full service gas stations are hard to make secret, hard to move elsewhere, this job was destroyed entirely.