> 100% profit margin [..]
That’s not how these things work
No. I got from the article that he's saying that the purchase is sunk cost, so any sale is 100% profit. So it's correct
that means $5 part is sold for $10. It's exactly how that kind of thing works
That's actually a 50% profit margin. Also known as a 50% markup, even though you marked the price up by 100%.
It's a 50% profit margin because the profit ($5) is 50% of the selling price.
It's a 100% markup because the selling price is 100% more than the cost.
Some people might call it a 50% markup, but that's purely a deceptive tactic, or just ignorance.