Well it depends on who's pencil is used and how sharp it is.
When retailer stores buy a product for $1 and sells it for $1.69 they call it 41% mark up. If I buy a bale of hay for $1 and sell it for $1.69,I say that I made 70% on the deal. If your plumber uses my siffering,70% sounds reasonable, useing manards' method 70% is too rich for me.

It's not 'overcharging'. It's markup for the time it takes to source, purchase and transport the correct parts for your job, as well as the experience and knowledge that it took for the licensed and insured professional to know that the diagnosis and prescription was correct for the condition.

It's the same as that $20 aspirin when you are in the hospital. Go to WalMart and $20 buys 20 bottles of 100 pills. Go to your nearest hospital, and have a professional assess your condition, diagnose it, and administer the correct drug. Then pay for the overhead and insurance for the professional and the real estate in addition to a portion of the medical school tuition and residency that your 25 minutes bought,. Then an aspirin costs you $20.

And yet they whine about a DOD procured $500 Toilet Seat... lol