Mid-term rentals can be a blessing if you have a hard to rent unit or are otherwise occupied with other projects and need to get someone in quickly. The way I do it is charge enough to get several extra months worth of rent.
Someone asked me once if I'd do a 9 month lease. At first I thought, "No way, I want a full year!" But then I reconsidered. The math is easy. Divide 3 months of rent by 9 and bump the monthly rate that amount. Now I'm getting paid for a full year's rent but only have an occupant for 9 months.
Example: Rent is $1000 per month.
3 months x $1000 = $3000.
$3000 / 9 = $333.
Rent for a 9 month lease is $1335 per month.
Here's the best part, if they change their minds and decide to stay longer and you decide to let them extend the lease, they're already used to paying $1335 per month, so the rent stay the same. Cha-ching!
My lease also has a provision that it automatically renews for a full year with a 2.9% rent increase if no one gives any notice, but if they want to go month-to-month they can request that in writing. If I approve, then there's a $50 processing fee to change their lease term (I have to write up an addendum) and a 20% rent bump. Not many take it, but some people do, and since I already got my years lease, then that 20% bump is a bonus for me being willing to be flexible. I found that if it's all spelled out in the lease, people are less resistant because they had a choice: they can either move, or go M2M with the 20% additional rent, or take the year extension. And since I already know the tenant, I know whether or not I want to approve a M2M deal or not.
This might not work if your state has rent control, but if you don't have that then yes, the short/mid-term rentals can be a nice way to increase cash flow without spending any money!
--184.4.xx.xx