First of all, a sidenote - In out playgroup, we don't break deals. At least nobody has broke one before, but I immagine if it would happen, I would probably just not make deals with said person in the future. You can, however, carefully word your deal. So, when making one, you should carefully listen the terms you agree to.
Scheming Symmetry:
Pretty easy one - You can offer a tutor in exchange for, lets say being not a target for a turn or 2, or if somebody wants to blow something of yours up, you can maybe sweet talk your way out of it with this - I've also been able to use it to deal with problematic card on board (let somebody else tutor for removal, while I search for something for my future set up, and still walk out of it like I helped the table) I am currently running this in my
Queen Marchesa deck, prefer it over regular tutors in that specific deck.
Orzhov Advokist:
I used to run it in the same
Queen Marchesa deck, but sadly, while I still enjoy the card, it didn't make the cut. I listed in here just so maybe somebody didnt know about it, cause it's still a sweet card.
Loran of the Third Path:
Pretty much the same use as
Scheming Symmetry. Not a direct tutor but what do MTG players value above all? Yes, drawing cards, so you can form some sweet alliances (to stab them in the back later on, when the time is right) Again, running this in my
Queen Marchesa and also in my
Kwain, Itinerant Meddler deck.
Humble Defector:
Only running it in my Marchesa deck. Basic set up is "If I let you have it, will you give it back after activation"
Duelist's Heritage:
Encourages people to attack others cause you can pump up the dmg. If they attack you - they do less dmg, if they attack somebody else, they will do more. Ofcourse you can just pump your own creature while attacking as well, but I mostly play it to start feuds on the field and encourage people to attack each other, not me.
Spurnmage Advocate:
This is probably one of my all time favourites. It discourages people to attack you with value creatures, and at the same time you have access to all graveyards for cards that are dealing with problems on the board. Need to remove a problematic artifact? Sure, hey, player B attack me with your weakest creature, I will remove it so player C can get his
Disenchant back from the graveyard etc. The possibilities are almost endless for this card to politic your way around the board.
Exchange of Words:
I am running this in my Kwain deck only, cause it matches the goofy vibe of the commander and said deck. It's a pretty recent addition. I've just found it fun to mess up the board state. You can, of course exchange the texts so that you get a strong ability for yourself, but just "Hey, thats a pretty strong creature player D is having, you want it?" is viable as well if you need somekind of immunity for future turns or need to get some kind of a deal.