Board Game Arena

You have misunderstood things. You are not allowed to play against the same people over and over, especially when there's an obvious and unavoidable difference in skill (and/or match throwing). Having a partner in Spades is entirely normal, allowed, and often expected.

Note, however, that partnering with another account you control is likely to get you in trouble sooner or later, as that gives you an unfair advantage (being able to see half the deck at once, instead of only a quarter).

I think the main thing is that for any moderation to happen, it must be reported. If you think someone is being "allowed" to break the rules, maybe it's because it was never reported. Other possibilities are that different moderators (or even the same at different times) may have different interpretations of the rules/guidelines, or that they had additional data to decide that was not against the rules.