I casually look through the foreclosures on Zillow and stuff, but they only seem to be listed around 5% off the estimated value.  

Scott The Book on Flipping Houses, The Book on Estimating ReHab Costs http://www.biggerpockets.com/flippingbookConsider checking out HUD homes for small multi's owner occupied gets first crack.

It requires a whole basket of skills and you have to be good at all of them including knowing your market really well, marketing skills (and significant funds), negotiation skills, understanding investment strategies and what makes an attractive deal, estimating rehab and construction expenses, estimating after repair values accurately and networking - to name a few.

Oh Zillow's estimates are generally pretty off base unless you mean you looked at other rental listings on Zillow.

Scott The Book on Flipping Houses, The Book on Estimating ReHab Costs http://www.biggerpockets.com/flippingbookCouple good reads 9 Reasons You Couldn't Find A Buyer For Your Wholesale Deal Don't Start Wholesaling Until You Read This: Wholesale Advice from a Fix and Flipper How to Start Wholesaling: Getting Past The Education and Into the FieldUltimate Guide to wholesalinghttps://www.biggerpockets.com/renewsblog/2015/01/31/ultimate-beginners-guide-real-estate-wholesaling-2/Download BP’s newest book here some good due diligence in Chapter 10.

Scott The Book on Flipping Houses, The Book on Estimating ReHab Costs http://www.biggerpockets.com/flippingbookConsider checking out HUD homes for small multi's owner occupied gets first crack.

Environmental Protection Agency estimates that toilets consume 27 percent of indoor water usage.Property managers and landlords sink 25 to 35 percent of their operating costs into utilities, while water costs, in particular, are up an estimated 200 percent in the past 15 years.Meanwhile, small, barely noticeable leaks may add $900 to yearly water statements, with larger leaks totaling, in some cases, $4,000.

How do you go about estimating the cost of repairs if you can't even inspect the inside prior to purchase?  

Scott The Book on Flipping Houses, The Book on Estimating ReHab Costs http://www.biggerpockets.com/flippingbookDownload BP’s newest book here some good due diligence in Chapter 10.

I have years of construction and house renovation experience which is nice because it makes estimating home rehab costs a whole lot easier.