Although the city sewer itself is pretty hassle free, it comes with being in a city and cities tend to be difficult to work with if you are running a mobile home or tiny home park.  

The going interest rate makes it seem difficult to cash flow $600/month.

One can imagine this makes it difficult (ie more costly) when adequate guidance is not given.

The first floor tenant was very difficult to remove but we finally managed to get them out with a cash-for-keys agreement.

The regulations have made it difficult for me to use this unit and to let friends and family use the unit. 

Rent control may prevent you from increasing the rent fast enough to keep pace with inflation, limit your ability to select a reliable tenant, and make evictions of non-performing tenants difficult or impossible.

Quote from @Charles Granja: Real estate is very difficult and capital intensive.

You could try to find more aggressive fixed income funds or ETFs, but transaction costs and market volatility could make your life difficult.

Insurance and interest make it difficult for the traditional lenders to loan to us even though we can afford the payment, but to them since we deduct a lot of things on our taxes, we don't look to be cash flowing.

They have made compliance so difficult that you should probably only do multifamily.