When that happens (max 3 times for me), I usually just give the player the win the 4th time I see the same lineup so I can assume it's the same person and most of the time, the same match stops.

But do you ignore the fact that there are others who want to finish the missions? If I see the same person multiple times, I know that they are trying to do their missions. If you figure out that your opponent is trying to do missions but you don't want to help them just because you are trying to brag/try out your team/bored or any other reasons, then you should listen to the people here instead of thinking about yourself.