Most real estate agents in the STL area don't do property management. If they tell you they'll find you a tenant (going rate is one month's rent), they'll slap your listing on the MLS and do nothing else. Because there's not enough money in it.
There are only two companies in the St. Louis area that I know of that do property management: West End Properties and Worth Clark Realty. These companies also sell properties, but that's not their primary focus. They'll find you a tenant for one month's rent. They'll also be the "property manager" for some fee, usually ab out 10% of the rent or thereabouts. The fee may depend on how much business you give them.
I once hired one of these companies to find me a tenant. My agent, who initially seemed like a reasonable guy, and I had differences on whom I should accept as a tenant. I ended up firing the guy and found my own tenant shortly thereafter.
If you recommend either of these companies to your friend, make sure he realizes that the agent's primary purpose is to FIND A TENANT - any tenant. And if that tenant doesn't work out, he will FIND ANOTHER TENANT. Because **he gets paid every time he finds a tenant**. So it's in his best interest to have to find you a tenant. Whether the tenant meets your criteria, or is a good long term tenant, is of no concern to the agent. This is what we affectionately call a conflict of interest.
I agree with Dave Ramsey that being an out of town landlord is being stupid. You just can't do it from a distance and if you try, things will likely not go well, sooner or later.