-Not taking proper care of properties, neglecting maintenance, ect-Trying to overcharge investors buy tacking on hidden charges such as a fee on top of maintenance bills.

As one client put it, "In California, tenants pay their bills in the following order: car payment, credit cards and, if they have leftover funds, the rent."

x2 on what @Bill S. 

A HELOC can be a very easy and powerful tool to invest in real estate as long as you are smart about it or you will loose your home and mess up your credit.  

In addition to market sense and people skills, REI also requires knowing what information is needed to determine feasibility, of acquisition, deal structuring, how and if to partner, building the right Power Team that wants to see you succeed and is not only in it because the/ she sees dollar signs.

I have heard a lot of people say they charge tenants for water but not too much about passing sewer bills on to tenants. my properties are all septic.Putting it on the tenant  means a backup is on the tenant but it is your property that would be damaged by  a backup. 

You want to use that information to check to make sure they have enough money to pay their bills, including the rent.

Can you bill back utilities? 

@Dennis Williams and @Bill F. - Confirming that the tenant is on month-to-month lease.

What about a security alarm system.I would tell them OK but if they really want them they will foot the bill.