I manage everything by myself. Many times, if property
manager find that you knew nothing about landlording, they will rip you off by creating many faked issues to get fixed using all kinds of excuses. Every repair paid by you will partially profit property management companies. However, if you know what must be done and what can be defered or not needed to fixed at all, they won't be able to rip you off. I currently get calls from tenant directly because I know must is my responsibility and what is not. I will only pay for the service that I may not have time to handle, such as going to court to evict someone. I only pay for what I need. Basically, the more you don't know about landlording, the more you would tend to rely on a third party manager, the more profit will slip into their hand...
To ensure success, you must learn landlording skills and associated laws. You can still hire extra hands to help you. But you can mostly avoid being ripped off.