What if anything is preventing a seller and end buyer "hooking up" and working a deal  after the assignment contract expires?

@daniel, il get into it as my driver loan expires in 85 days, I'm all in on this company n nothing much left to invest right now, 15% to good to be true but 5 days had past by, 85 days to go.

you cannot change the rent in the middle of a lease term. if they are month to month or nearing the expiration of the lease you can simply send them the proper notice.

If the landlord does not give such notice then the tenant can move out at the end of a lease without notice.Solution, require 55 or 45 day noticeHere's the law:504B.145 RESTRICTION ON AUTOMATIC RENEWALS OF LEASES.Notwithstanding the provisions of any residential lease, in order to enforce any automatic renewal clause of a lease of an original term of two months or more which states, in effect, that the term shall be deemed renewed for a specified additional period of time of two months or more unless the tenant gives notice to the landlord of an intention to quit the premises at the expiration of the term due to expire, the landlord must give notice to the tenant as provided in this section.

Do I wait for their lease to expire?

@Vanessa Garcia your idea about chasing expired listings is a good one.

The leases expire next June, and in order for the bank to underwrite the an owner-occupied loan I need to move in when the lease expires.

Depending on where the property is located, that mortgage will not expire until X years after the maturity date.

Many times the homeowners have moved and forward address expired but on the label it will list the new address   Also you can skip trace the owner knowing that the address 90 percent of the investors are mailing to is not reaching that owner. 

Even with all this capability, what may never expire is the need for customer service in business and the guidance in an unfamiliar time such as buying your first home or buying your forever home.