@Nathan Gesner given that you work in property management I'm sure you know the industry better than most of us but I thought I would make one comment. If the margins are so low, which I believe you that they are, then why is anyone doing it? Maybe this will add some insight @Michinori Kaneko. From my observation most small management groups fall into managing other peoples property because they are already managing their own robust portfolio and they see the big cash in the power that bigger management comes with.
Since property managers usually manage their own property they get the cost of what paying someone else for management would be returned to them. That could be reason alone but it isn't. It also means that they sit at a great pivot point for economies of scale on all kinds of things and they are a magnet for good deals. By the time you have hundreds of properties and units you manage/own it starts to become cheaper to hire your own handymen, plumbers, rehab guys, etc. You can pay them a wage for their work and then charge extra on their services to your clients so that you are making income off of every service that is provided. You have control of their labors so that if there is an emergency at your own properties or those you manage you can direct them there instantly, saving time, damages and money and keeping tenants happy. You can also more effectively develop relationships with suppliers, titling companies, real estate agents, banks, wholesalers, insurance agents, law firms, service providers, government housing authorities, inspectors etc etc.
There in lies the true power of economies of scale. Hypothetically If I own 5-15 duplexes representing 20-60 tenants in a community and especially in a city, very few service providers and suppliers care about what I am doing. On the other hand if I represent 400 units and thousands of tenants I've become a relevant factor in almost any market and people are seeking my business which gives me negotiation power.
IMO the biggest benefit to property managers appear to be the ability to naturally land lucrative deals on properties that only come to them because others in the market know they have influence over a large group of investors. They get approached by bankers, wholesalers and brokers looking to unload numerous foreclosed or brokered properties quickly. This benefit cannot be overstated because managers attract these deals like flies and they can pivot to either collecting the most lucrative deals for themselves or making margin in wholesaling to their clients.
I was with one property manager when he got a call and email from a bank that they wanted him to bid on 20 residential duplexes and single homes. We went and looked at about 10 of them together. It was like a million dollar deal but he was confident that he could turn around and resell them to his clients before the deal even closed while keep a couple for himself. The same day we had to visit one of this guy's personal property for a showing. It was a huge 3 unit apartment building where each apartment was about 2500 square feet. He had bought the property for something like $60000-70000 and each unit was making around to $2000 rent. He told me his return was about 50%. I was blown away on how he could get that deal and he just said contacts come to him with deals all the time and now he doesn't even keep anything that isn't going give him a 30% ROI. Anything less he just resold to his clients.
Years ago I wondered how property managers can do what they do on the small fees their receive. Now I see management and associated fees as the tie between the manager and the investor which enable them to take advantage of the market in all kinds of ways. This probably isn't true for all managers but I don't know how many of them are even making it otherwise.