As a guest, when you book for the first time, it can be helpful to use an online travel agency such as VRBO or AirBNB. You can read the reviews and have the peace of mind that the property is as described, and the experience is unlikely to disappoint you.
For this, you pay a substantial service fee, between 10-20% of the booking amount. The online travel agencies provide a service, and invest in marketing, and arguably earn this fee for this initial booking.
However, if you are return to the same property, or can do your homework and feel comfortable with the host, why would you want to pay this fee again?
You can save the service fee, and still have the peace of mind that you will have a great experience.
Great hosts take care of their guests, with or without the online travel agencies.