Sure, I also need paint, but I go to the hardware store and buy the cheapest I can find, while a painter really uses good paint that is correspondingly more expensive.
Doing something like this yourself is no problem - if you don’t hate it like others here ;) but if you work cleanly, cover everything, and so on, then no difference should be visible.
It just takes longer when you do something like that yourself, because professionals are of course already experienced. But I enjoy it, so I'd rather save the money.
I let painters in my old apartment and in my new one I did it together with a few friends. -Maler-Party :) It was super fun, you can't see any difference.