Why you should avoid everybody speaking of "amateur" screenwriting:
Because that's the hallmark of every fake or bad professionals. No true professional will speak about what an "amateur" does or looks like for one simple reason: the only thing that matters is the story.
Let's be clear. There are only 2 reasons why people use the word "amateur" about other people:
1. They need to feel themselves better than they actually are,
2. They want to sell you something and talking about what an "amateur" does or doesn't is just a way to tell you "you are an amateur and I am a professional / an insider / a gatekeeper / the one who will give you the key of success, so give me your money and I'll teach you what you must do or be", which is a lie.
They are thousands. Four come out every time you kick a pebble.
Actually, 99 percent of these people never wrote a single script up to the end of the first draft. At most they read tons of screenplays for a few bucks among other jobs to earn a living.
So they focus on nitpicking details: the use of "cont." or not in formating, all the storytelling stuff you should avoid to use like alternative structures, flasbacks or flashforwards, the use of adjectives and adverbs, the use of passive verbs... They recomand you the use of subtext, caracters' arc... although only a few could find and explain subtext or characters' arcs into a script, and even less could show you some ways to use them.
The only reason why these people always give you the "why" of rules but never teach you the "how" is because they just don't master the "how". And that's a shame. Because these are wonderful tools that every good writer uses to make their stories better.
Would you learn playing violin with somebody who doesn't play violin? [ ] Yes [ ] No
At best, they could tell you when you make a bum note. But as they'll never be able to teach you how to play it right, they'll just teach you how to avoid playing it, which means not to play most of the music you could.
So if you meet some of those people, don't let them trick you. You are probably worth better than them.