Something about unwritten rules

[ruzota]

Explain me please why some other players say they will file a complaint in the game of Catan when they see that my partner and I are playing together? Is this prohibited?

[Phoxtrot]

If by together you mean "at the same table", no it is not forbidden.
If by together you mean "playing as a team", then yes, it is forbidden. (Unless, of course, playing formally as a team in a game with an official team mode)

Also, I don't know if there is anything explicit about it but coordinating with someone to try to be at the same table in Arena mode can be conspicuous.

If you often play with the same people, someone, at some point might analyze your games and see if you seem to systematically "go easy" on one particular player while playing more aggressive against everyone else. That is implicit collusion and not allowed.

[euklid314]

Explain me please why some other players say they will file a complaint in the game of Catan when they see that my partner and I are playing together? Is this prohibited?

I only looked at one game of yours (#484409207) and yes you made two very suspicious trades right at the beginning. These trades were very unfavorable for you and helped your friend to build two settlements.

This is ELO cheating and of course not allowed (see written site rules). If you keep playing like this you can be reported, moderated, get punishments and finally bans.

If you play with your friend you have to treat him as an opponent like any other opponent. If you find that difficult, don't play with him again. You cannot play 2 vs 1 on BGA.