For the average buyer, sooner or later you are going to hit a wall with your DTI.

Than I thought it was all the things that could go wrong in the flip, hidden gems like K&T hidden in the walls, shot main-lines, etc.....   

Quote from @Account Closed: I would say.. can you save the tub and re-glaze and redo the tile on the wall can save you $1,000 or more just on materials and labor..

The only deal I’ve ever walked away from we determined that the entirety of two of the exterior, structural walls were significantly bowing and in the basement below them the foundation had been permanently covered so there was no way to see what it was doing.

@Dani Beit-Or  Yes, nationwide/Wall Street backed lenders offer HELOCs on investment properties. 

@Jaron Walling, Thanks for that shout out. 

Moving walls usually requires figuring out what is or isn't load bearing and likely putting a large and usually expensive header.

Paint walls, make sure everything is in great condition.  

Even wall st guys miss  these things  right . 

Real estate's "gross rent multiplier" is Wall Street's "sales to revenue",  "cap rate" is roughly "P/E ratio".When evaluating markets and investments I tend to start with GRM (or lazily the 1% rule), then attempt to return a cap rate based on assumptions about costs, then I work my way to multiple years of projections (assumptions about inflation, amortization, tax benefits, etc), and if I am partnering with one of my smart friends I have to pull up an IRR (internal rate of return).I also look at regional employment levels, median income to rent ratio in the zip code etc.