How do you deal with collusion?

So, i decided to commission my first league with teammates from my football team. We put in £10 each and things were fine for quite a while. There’s been a few issues since with very odd trades and i’ve brought this up with the rest of the league and had them vetoed. This week though, one team decided he would get rid of Barkley for Josh Adams and Chris Carson. Again, i brought it up with the league and the two teams involved tried to justify how this was a fair deal?! He eventually admitted that he would have given Barkley to anyone that had asked, because he was no longer in the running? The trade eventually got vetoed, but this is becoming very frustrating and makes the league very contentious. I’m in with a chance of playoffs going in to the last week, and i don’t want to fold the league at this point. I already won’t be creating a league with the same people next season, but is there anything i can do to make sure this doesn’t happen again?

I would say first of all, get a trade deadline set up for the right date - early enough that most of your league will still be in with a shot of the playoffs and therefore be active and competitive in trades/moves. In my main league, the most completive home league we find that week 10 or 11 works well, 11 for the last couple of years has been fine. We have playoffs in week 15 and 16 but if you start in week 14 i would say have the deadline in week 10 as three weeks out is close enough to the playoffs.

The money aspect is a good move and it should again keep people invested in the their team and as a result benefit the league. The overall prize is good, i would maybe look (depending on budgets and how much everyone wants/can put in) at having weekly prizes for top scoring teams and the overall top points scorer then 1st, 2nd, 3rd place or just 1st if you are doing these weekly prizes. That should keep people more honest in playing the best team each week as they always have something to play for even in last place! I say top points scorer as well just as on rare occasions the top overall scoring team can miss the playoffs unless you have wide brackets or rules for them to get in (happened this year in my home league).

Those would be my starting points, also if you wanted to establish some rules pre season for the league you could go down the route of anyone who is mathematically eliminated before the deadline will not be able to make any trades of any kind to remove any option for roster poaching from the top teams. Some will say they shouldn’t be allowed to make roster moves at all (waivers and free agents) but i think that is wrong and fair game if they want to make moves plus if you have weekly prizes they should be able to make waiver claims at least - but not trades if you are out of the running that leads to grey areas and issues.

Hope some of these help and the trick is not having too many rules that it takes the fun away, unless its a hyper competitive high stakes league you just need a few in place in the casually competitive home/friend leagues to keep order and stop the obvious issues each year and make sure everyone enjoys - plus keeps you the commissioner mostly headache and hassle free!