Is it legal to allow free rent agreements as part of a real estate transaction in Monopoly? Specifically I'd like to purchase a property and sell two additional properties but only if both parties in the transaction receive 'free rent' as long as we own the properties.
You can offer a rent free situation by promising the player that you will never claim rent. As rent is only ever paid when the owner of a property claims it, you can in effect offer free rent.
There is no way to enforce this though and you must treat this as nothing more than a gentleperson's agreement.