Training plumbers
Some places have master plumbers, other places call them "residential plumbers", min 6000 hours with a journyman before you take the test, and "commercial plumbers" min 8000 hours before you take the test.
We do carry cards and keep them current.
I would say I learned more about plumbing after the first five years.
The first five years was like basic training. You still didn't know much.
When I started my training, along with about thirty others of similar age, the main purpose of the trainers, was to see how much we could take without quitting.
Most of us were married, and some with kids, so quitting for most of us was out of the question. I've never been in boot camp, but I would guess it was somewhat along those lines. The first week in the field, was picks, digging bars, shovels and sledge hammers. To make it more enjoyable, the Journyman and the apprentice insulted and made fun of us.
They didn't want to waste their time training you if you were going to quit on them.
It was also payback for how they had been treated.
The first week, my hands were so sore, I couldn't close my hands.
After the first week, my hands got used to it, and I started picking up speed.
Common injuries became smashed fingers, cuts, and burns on face and arms.
On some job sites, I would wear rubber boots when my knees were causing too much pain, then when my arches were giving me trouble I would switch to stiff boots. In the Winter, when the rains came, there were times when you would get shocked if you forgot and touched your knee to the floor while drilling.
Working with 1/2 hp drill motors that would break studs in half, you tried not to get your chin hit when you hit knots and nails that were hidden.
I think the worst for me was dislocating my shoulder every so often.
The pain from that made sleeping difficult.
Try crawling a crawlspace after that.
I could still knock a hole through a 8" foundation in five sledgehammer blows or less though. When my arm was good.
From a business standpoint, what the homeowner is seeing in pay, is not what the plumber gets to take home. The owner of the company has a lot of uses for the money that is billed.
Part of what any business does, is having a structure that operates within government guidelines.
You will have business licenses, taxes, advertising, vehicle expenses, tools to be bought and maintained.
Insurance, workmens comp, health plans, phone bills, gas, repairs, time out to keep stock, dump runs, answer phones, order materials, explaining things to workers before they leave for the day. Book keeping, tracking receivables and payables.
If you're doing service work, you're lucky to get four billable hours a day per plumber.
You pay him for eight, he gets you four.
With contract work, where he may be working the same place for days, it gets better. More billable hours, and typical for the contract, less per hour.
Homeowners may be confusing a billed rate to a working wage.
When an airplane is sold, the pricetag is in the million plus range, the workers don't get all that. The business that builds the plane may only be making 3% which is a very small margin considering that everytime you pay with a credit card, the business owner has to pay between 2% and 3.5% of the total amount charged to "card services".
There are many places that the money goes to.
If you want to charge $150 an hour, show me your master plumbing certification 
