You're right, some of those examples you gave have varying levels of being problematic. I just would draw the line at a different place than you would. I would not allow a married couple or any two players who are known to share the same bankroll, in the second manner I described above.

This is assuming the game is big enough that it is possible for players to make a decent amount of money through collusion, and that other players don't like them being allowed to play together. If none of the other players minds them playing together then I wouldn't prevent them from playing together.

what are the stakes? what exactly did they do?

It’s a $5 bring in plo game that can get quite large and multiple $1,000s scores are common. They soft play and according to one reg have signaled to each other in game (I have not verified the last point).

how does a married couple soft playing hurt anyone? ive played in this exact scenario and it makes them incredibly easy to read.

If you're not a regular and don't know they're married, it could give you a really biased perception of how they play in general.

yes, but two people who soft play each other (never bluff each other) are very easy to play against even before you know exactly what is going on, no? id love to play at a table of people who never bluff in 3 way pots.

I've stated plenty that if I know (or feel) that Players are working together then I try to wield that to my benefit.

Where I feel the line is FOR SURE, is the signaling. Soft Play is one thing, but if Players are actively signaling or using a bet/cold 3-4 betting strategy then they need to be called out. The bet/cold raise spots don't really work to well if they sit next to each other since it doesn't generate any extra dead chips, but it can be attempted. In the home game where I feel this was happening the two Players 'actively' never sat within 3 chairs of each other, if they could help it.

There are Regs in our game that if they end up HU on Turn, then the River can be very passive. But, IMO, they aren't actively seeking out those spots .. it's only reactionary once the situation pops up. GL

I can't imagine that was what he meant. Anyone I have ever seen soft play still play normally when the pot is three ways.

I agree with a of this.

I would also say that if I am at a table where two players make it clear they have a prior relationship, I think it is imperative to find out what that relationship is and how it affects their play.

For one, (obviously) making sure they are not openly cheating. I will specifically look for signals or tells between them.

More importantly, to see how it affects their play. For better or worse, players will play differently against players they have a relationship with. It make be subconsciously deciding to call with pocket Jack's rather than reraise, or it might be even result in more aggression instead. Some way their play will change. I want to know how.