I treat the "we want people who know stack X" kind of thing as a "Here's what stack we are using" and nothing more. I don't lie and say that I know the stack, but I don't want to work for a company that doesn't understand that a good programmer can switch to a new stack in a very short time frame. On the other hand, you need the ability to pick up a new stack easily.
I hire contractors. I don't have time for people to ramp up on the job. I need them to come in knowing the stack we are working in. If I were hiring full time devs, I would take a chance but I would expect them to meet deadlines as if they were fluent in the stack - meaning if they have to work weekends or more than 40 hours a week to be just as efficient as someone who knows the stack, they should do it. I put mysel…
Then if I get stuck at something I'll try to fix it first, then learn more about the stack to see if I'm missing something basic and finally ask for help. These go normally for free if it's because of my lack of knowlege; otherwise I'll charge for them ofc.
I've also found out it's quite important to explain this to whoever is hiring you. That way they don't feel cheated on (money) nor like you are slacking off and working only X hours instead of 2X per week.
PS, your comment sounded quite negative/exploiting, probably that's why the downvotes.