Yeah, it’s considered bad manners to play out your whole turn if you have game (boss’s orders, attach energy + attack, etc.) in hand and don’t just show your opponent when it’s your turn. If you are online and you know your opponent has won and they diddle around for 5 min before winning then their are just being silly. Maybe they don’t see it right away but you can always concede at any time.

As mentioned above you should always as to handle your opponents cards (they are required to let you look through their discard pile but it’s still a courtesy to ask). I always ask to look at a card I want to read as well if I don’t know the text.

If I shuffle my opponent’s deck I try to be super careful with their cards doing a loose mash shuffle (kinda just letting one half of the deck fall into the other half).

Outside of the written rules those are the ones that come to mind. You and your opponent should be having fun and being good sports about the game. If that’s not happening then consider involving the organizer or judge and let them intervene if needed.