Here's what I would make sure of:
1) Monthly income needs to be greater than 3x the rent amount ($900/month rent x 3 = $2700/month minimum income). Get paystubs from employer and call the employer to verify that they work there and are in good standing
2) Verify their rental history. Call their previous landlords and see what kind of renters they were. If they can't provide that to you, make them pre-pay for the last month's rent with the security deposit and the first month's rent. It's more risky renting to people who haven't rented before or who can't provide landlord contact info.
3) Don't give them a key to the house until they transfer the utilities into their name and ask for proof (account numbers). If you give them the keys without doing that, you could get stuck paying their utility bills
