What's your motivation for asking this question? There are a number of solutions that solve problems around listing, credit checks, paperwork, etc.

The thing that pisses off landlords the most is problem tenants. The ones that don't pay and/or damage the property. In tenant-friendly states, the eviction process can be long, complicated, expensive and riddled with pitfalls. Additionally, there are "professional tenants" out there who try to game the system by legally squatting.