New 4 Plex with 2 leases expiring before closing

[Cody Harmon]

Hello,

I am looking to put an offer on a 4 plex in the next couple days. The listing agent provided me with the current leases for all the tenants, and I noticed 2 of the contracts expire in about 20 days. Rent has risen drastically in the the area over the last 2 years, and I was counting on raising rent a bit on 3 of the units including the ones with contracts expiring right before I take ownership. One of the tenants has been in for a long time and I am wondering what could stop the current landloard from theoretically lowering the rent 15 days before I take ownership? 

Can I write anything in my offer letter stating that the offer is based on no new contracts or contract modifications being negotiated with any tenants from the date the offer is submitted until I take ownership?

Thanks!