Can a $100,000 single family house really cash flow ?

Tonight, I went to seminar presenting opportunity investing in Dallas single family house (SFH) opportunity. House price of a 3b2b is around $100,000 and the rent is around $1000 dollar a month. At first glance, this look like excellent postive cash flow producing property. This is the breakdown of the calculation
Rent: $1000
Mortgage: $525 (assume 7% interest only, 10% down pay)
Insurance: $50
Tax: $250 (assume 3% of property tax)
Total PITI Expense in this case is $825 per month
So, the positive cash flow we're looking to get is $175. Multiply it by 12 , you get annual income 2100 a month. Dividing 2100 by 10000 to calculate your return of investment (ROI), you get 21%. This seems VERY Impressive. Plus, the potential of the house price appreciation over years in future. Look like a deal!?
But wait, let's look into further, first since I will not be managing it myself, I will need to hire property manager to take care renting. 10% of the rent is deducted. This reduce your annual income to only $900 and ROI to only 9%. Well, it's still ok, at least it's still comparable to stock market average return. But, here comes the BIG BUT, there could be unexpected expense that can pop up once a while and eat up all your cash flow. EX: A roof repair cost 2500, a carpet change needed cost 750, a paint need to be repaint once a while cost 500, heater breakdown cost 300, a window issue cost 350, a foundation problem cost 3000, the list could go on and on and on.... So, I'd say the reason to buy this deal should not be purely for cash flow. The profit is too slim to see them working. We should look more into the equity build up potential as a consideration and investment objective.