Sometimes those can be substantial, especially as you will be managing 3 tenants' sinks, toilets, disposals, etc.

They also put in service requests to fix the garbage disposal, replace light bulbs in the kitchen, replace window screens so their cat can sit next to any window without being able to escape outside, and now replacing the AC. 

Another issue is that short-term discounted cash flow has become the standard way to measure the success of income-generating development, resulting in "disposable" suburban designs that make money in the short run but are not as successful in the medium to long term as walkable, mixed-use environments.2.)

Different states have different laws about if and how long you have to keep tenant property along with what kind of property you keep and what you can dispose of. 

May be too old and needs to be bulldozed but no one wants to deal with the hazardous waste disposal.

The Court will require the personal representative to file a report to advise of any claims filed in the probate estate, and will not permit the probate estate to be closed unless those claims have been paid or otherwise disposed of."

I also add up their current payments on all debts via the credit report, the rent payment, utilities and others and then use that final number to subtract from their net income to get an idea of what their disposable cash position is each month.

@Michael Randle CapEx (Capital Expenditures) are those costs which, when incurred, will be amortized over a fixed period of years (Roof, new electrical, plumbing, windows), where as repairs, as @David Faulkner pointed out, are minor and are expended in the year they occurred (leaky faucet, new garbage disposal, clogged sink/toilet, one broken window, etc).

The biggest thing is make sure they are a reputable company that will dispose of the heating oil or recycle it. 

Sometimes the labor costs (removal, installation, disposal) can skyrocket on high-rises.