Skek, if your property manager is charging 15%-20% off rent, you got ripped off. Most will charge 6%-8% around here. Certain locations will charge more, like Las Vegas.
Finding a good property manager is very important. The experienced ones can hold a short conversation with the tenant and immediately spot all the alarm bells. If you have the empathy skills you can try to do this yourself, otherwise it's better to find someone to do it for you.
As a landlord you don't want to try to maximize the monthly cash flow. It's more important to keep a good tenant. You're entrusting property worth hundreds of thousands of dollars to a renter, it's quite stupid to try to squeeze an extra $50 to risk losing a very good tenant. Because if the property sits vacant for just 1 month, you'd lose more than what you're trying to make.
A property manager will be responsible to the tenant's needs, and repair anything that's broken. This means, if the dish washer broke, the manager will call someone to go fix or replace it at your expense. As the owner, you'd also have to pay renter's insurance and put your property manager as a covered person. There are all kinds of expenses (carpet cleaning, painting, advertising, etc) that you (the owner) will be liable to pay. It's better to listen to your property manager and not try to save pennies.
Anyone who has the $ can be a landlord, but not everyone can be a good property manager.