Some tax software like TurboTax , or professional services if you are too concerned,   can do it for you in a more accurate way . 

You should look at AVMs see if the asking price and rental price are accurate before making an offer using Zillow, Redfin and rent sites including Craigslist. 

That couldn't be more accurate.

Also make sure your ARV estimate is accurate.  

Just request that you sign off on the numbers as true and accurate per the information you received.

There are those who would say that investing for appreciation is either speculating or gambling, not investing.

@John Choe, What I do with potential clients is sit down and have them pencil out their income/expenses/allowances on the property they're wanting to sell so they can have an accurate picture of what they're true income/return really is. 

They all require an underwriting period to determine if they'll even lend on the deal, and do so based on the Asset unlike traditional financing.So BP,  how am I supposed to accurately determine (or at least ballpark) repair estimates, so I can make a sensible offer and respect my General Contractor's time? 

Assuming my numbers are somewhat accurate this purchase will cost you at least $500/month initially.Without a significant value add, it is likely going to be many years before you have any return on your investment. 

It's not the most widespread way to sell a house, but there are tax advantages to those who would prefer them and don't need the money, there's contract for deed options for those purchasing low cost homes, there's people like myself who would like to purchase a property, rehab and sell it on seller financing...I think it's more accurate to say that there are newbies who hear about all these creative financing methods and think it's their way in when in most cases they are best reserved for more experienced investors.