All you need to do is thoroughly review whatever agreement you signed (presumably the lease) when you first acquired the place you are renting. There usually are some sorts of provisions in there for breaking the lease.
You should also do everything in writing. If there are additional requirements that are not specified in the lease get it down in writing. For instance if this 30% fee is not called out in the lease, make sure it is in writing. That includes the method of how it is paid, whether it is deducted from the deposit or not.
Don’t worry about the “who” you need to be protected from, worry about the documentation as that is what obligates you. You are not obligated by any more, or any less then what is on the document, regardless of whether the party is the owner of the property or the landlord. Relying on anything verbal is a bad idea.
