Clearly need to make the purchase contract subject to the lease and possession subject to the lease. Landlord/Owner needs to transfer any and all funds held pursuant to the lease to the Buyer at closing. The lease also needs to be assigned. Sometimes you can negotiate with a tenant to move out before the lease terminates. This may cost some money, but may be worth it to the buyer and seller. Also, get your owner/seller to incentivise the tenant tenant to cooperate with showings by offering a couple of hundred dollars if the tenant cooperates by allowing showings, keeping the place neat and clean and if a prospects asks them questions to be professional and positive.