A lot of my online gaming experience comes from computer games, and so things like saying GLHF (Good luck, have fun) and GG (Good game) pre and post matches, is second-nature. I just think it is good sportsmanship and to me it matters not whether the opponent is the same. I had one guy constantly trash talk me in chat the whole game, "OMG, you think so much and are still losing!" "What if this was Blitz Chess, move faster!" just on and on, and when he won the game I just said GG, Thx! and so in that regard I would say, have a thick skin. You are playing competitive games with people, some of them will be nice, some of them will be jerks.
With respects to rematches, if I win a game within say 6 or 8 moves because my opponent just didn't see one of those basic early-win scenarios, and they offer a rematch I will most likely accept. I mostly decline rematches due to time reasons - I play longer time-control games, and don't often want to embark on marathon Chess sprees. :) But I don't think its rude to decline a rematch as a standing rule, like, you are playing online - people have lives and might need to go put the washing out or something else equally as exciting. ;)
I would like to add one item to this list of moral quandries - Takeback Propositions. You might encounter this a lot on Lichess, I know I do. I used to accept these from opponents, but I do admit that I started getting annoyed when I let them take a move back, and then I ended up losing. I've never asked for a Takeback and tend to feel you should live with your mistakes as that is the best way to learn - feel the pain of dropping that Queen or whatever. So my stance at the moment is that if it is a Rated game, then no Takebacks. Casual game, sure go nuts I don't mind. Exception being if for instance, a piece is clearly going to take one of my pieces, and it stops a square short, then my opponent says he mis-clicked or whatever. I can believe that, I've done that too where I drag it quickly, especially in Blitz and release it too soon and I end up standing my Queen right in the firing line of a pawn, rather than capturing the hanging Rook say. That is more credible to me at least.
Hope that helps!
With respects to rematches, if I win a game within say 6 or 8 moves because my opponent just didn't see one of those basic early-win scenarios, and they offer a rematch I will most likely accept. I mostly decline rematches due to time reasons - I play longer time-control games, and don't often want to embark on marathon Chess sprees. :) But I don't think its rude to decline a rematch as a standing rule, like, you are playing online - people have lives and might need to go put the washing out or something else equally as exciting. ;)
I would like to add one item to this list of moral quandries - Takeback Propositions. You might encounter this a lot on Lichess, I know I do. I used to accept these from opponents, but I do admit that I started getting annoyed when I let them take a move back, and then I ended up losing. I've never asked for a Takeback and tend to feel you should live with your mistakes as that is the best way to learn - feel the pain of dropping that Queen or whatever. So my stance at the moment is that if it is a Rated game, then no Takebacks. Casual game, sure go nuts I don't mind. Exception being if for instance, a piece is clearly going to take one of my pieces, and it stops a square short, then my opponent says he mis-clicked or whatever. I can believe that, I've done that too where I drag it quickly, especially in Blitz and release it too soon and I end up standing my Queen right in the firing line of a pawn, rather than capturing the hanging Rook say. That is more credible to me at least.
Hope that helps!