There are some career paths where "fake it 'til you make it" is a viable strategy to get ahead. Some of my favorite musicians stole songs from other musicians and made millions.
Sometimes this worked out for them because they were related to, friends with, or married to more powerful people who ran interference for them. Sometimes this worked out for them because they were the correct complexion or gender. So it goes. Life isn't fair.
However in today's world it's easier than ever to check up on someone and verify that they have the credentials they claim to have or have created the work they claim to have created. So regardless of what people have gotten away with in the past, it's probably the best move today to be honest about things like credentials and creations.
Jumi Bello, an aspiring author, learned this the hard way. Bello, forced to admit that portions of her debut novel were plagiarized, wrote an explanation and mea culpa that were also plagiarized.