I have a few tips:
1: Give your opponents respect. Don't call them a scrub unless they are a scrub:
http://www.sirlin.net/ptw-book/introducingthe-scrub
If they don't do advanced tech because of a BS honor code, then don't call them a scrub. They are just lowbies and/or casuals. Don't resort to derogatory terms just because you are upset that they are giving you a hard time.
2: If you are being beaten by lowbies you shouldn't consider yourself to be much better than them. I know exactly the stage you are in, that weird middle area where you know some tech and can play against competitive players and do fairly well, but you still somehow lose or struggle with people that don't use any advanced tech.
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There is a simple reason for this. You aren't actually actively playing. You are just auto-piloting. You aren't actually adjusting to your opponent. You expect your opponent to play a certain way, and when they don't things are breaking down. In order to beat them you will have to first learn how to observe your opponent, and then you have to learn how to adapt to their play style. The good thing is, lowbies like this are the perfect opportunity to build that skill, as they tend to have tons of errors in their play to exploit.
Some things to watch for in a match:
Do they tech? At lot of lowbies never tech, and if that is the case you can easily just smash the moment you knock them on the ground.
Do they sweetspot the ledge? It's highly unlikely that they do, which means that the most basic of edge guarding will destroy them. Secondary to this is do they tend to recover high or low.
Do they have glaring habits? The answer to this is yes, because they are patiently waiting to f smash you. F smash is pretty much a terrible move to just toss out in most cases. You know that they plan on f smashing you, and you know that they plan to do it when you get close to them. Why can't you adapt to that? There isn't a point in saying how to beat that, because other people have already mentioned things, but it's also no point in doing it because it's so obviously a bad tactic that you shouldn't be falling for it.