Justin,
Some of the things that we put in place that our clients seem to enjoy are:
Lease Guarantee:
Ask if they offer a Lease Guarantee. If the first months rent is going to your manager you should have a guarantee that the tenant will stay for their term or your money (or a portion thereof) will be refunded.
No Security Deposit Admin Fee:
This is a bogus charge. Several companies say they are charging this to the tenant.
Example: Security Deposit $1500 / Admin Fee charged to the tenant (from their deposit) $150. Applicable deposit = $1350. Now technically it was charged to the tenant, but if the tenant damages the property, you only receive $1350 instead of the full $1500.
No Lease Renewal Fees:
Many companies will charge you a fee (as much as 1 months rent) when a tenant renews their lease. A small admin. fee is acceptable, but anything more than that is rediculous.
Online Payment Options:
The check is in the mail just doesn't seem to work anymore. Online payment options gives your tenants that procrastinate the ability to pay at the last minute at their convenience.
Make sure the Property Manager is not managing property part time. This is a full time job.
Make sure they have their network in place...Accountants, attorneys, maintenace crews, etc.
The list can go on and on, but use your gut.
Here are a few things to get you started.