I usually do 2/3, sometimes more. (Maybe 3/5 sometimes) I am somewhat guilty of doing that a couple of times, but who knows what problems others may have? Also, I tend to like diversity, so I'll get bored against those who play Zelda for like 4 matches.
I'll definitely disconnect from a match that lags badly, though; I don't think that's fair for either of us to experience.
Overall, I wouldn't say that it's a bad thing in itself to do this, but it's more courteous to not do that in optimal conditions.
Sometimes people leave to say "HA! Got that win; screw you I'm out!", but other times they genuinely don't have time to play much, or they don't have any disrespectful intent by leaving (some may want to simply fight a new person each time, regardless of skill but not be aware that the previous person wants a rematch).
Overall, I won't hate anyone for doing it to me, as there's going to be many more matches to come for me (I couldn't personally care less about my record), but it'll give me a slightly brief feeling of saltiness during those times that I may actually want a rematch, but those will be ephemeral at best.
This thread has also made me aware of the little things you can do online that aren't sporty, so I'll definitely take note of it. (Maybe even make an online etiquette thread!)