wow! never say never good luck to you
best of 3 should be complusory!

wow! never say never good luck to you
There is no luck in chess, so you are supposed to tell your opponent, "good luck". But, don't say "good game," if you beat me, because it was obviously garbage on my part. I always say good game after my opponent drops a queen.
In other words, don't take yourself so seriously. This request for rematches is an example of taking yourself too seriously. Just play chess. If you play enough, you will play the same opponents multiple games over time. There's one player here I've played over 400 games. I do know him IRL.

I just blocked an opponent who tried to run me out of time in a dead drawn ending. I played the last fifteen moves in 5.5 seconds after he blundered away the draw. We have played three games. Two lasted more than 75 moves. I have 2 1/2 points. We will never play again.
I don't give any rematches and I don't ask for any. That's only fair. If you feel you can play better, you should have done your best and played better in the first game.

wow! never say never good luck to you
There is no luck in chess, so you are supposed to tell your opponent, "good luck". But, don't say "good game," if you beat me, because it was obviously garbage on my part. I always say good game after my opponent drops a queen.
In other words, don't take yourself so seriously. This request for rematches is an example of taking yourself too seriously. Just play chess. If you play enough, you will play the same opponents multiple games over time. There's one player here I've played over 400 games. I do know him IRL.
I've played the good old @MSC157 exactly 400 games. scoring an amazing 29%.
Best of 3 means someone plays white twice. You have no honor. And why should white go first, you racist.
Sorry but I'm required to overreact by chess.com's unwritten defacto TOS.

too many players are leaving when they win, i always offer a rematch!
I have simple common sense rules when it comes to online chess:
No chat, no rematch.
If you don't have the time, desire, or just plain human decency to type "gg" "good luck" "hi" "hello" or anything else like that. Don't expect a rematch.
If you're ego bruises easily? Try something else besides an online game to sooth it.

If the game is actually a good battle—something rare at my level—I write a note.

If you want to play a match, ask a friend, they'll probably play a few games with you.
If you're playing strangers, then like Ziryab said, something about don't have an ego, and just move on to the next game.
Often I have time for one game. More often I have no interest in another game with the lousy player I just beat. No worries on your part, though, we won’t ever play.