Hi @Billy Rowe , good question! Much of this depends on why you are buying the house. Is this a flip or a hold for rental? Are you buying to live in? This affects the math a bit.
For most investors, I'm not sure the price/SF is the best approach. It is certainly an indicator, but you have to know that the comparable properties are indeed that, Comparable. But you DO have to determine the value (most commonly referred to as the ARV = After-Repaired Value) before you can determine what you will pay as an investor. I've never heard of the 10% discount rule, but once we determine the ARV, we use this formula: ARV times 65%, minus repairs = Max Offer. This is a MUCH deeper discount than 10%. But we are buying as cash investors. We would get laughed out of most offers if we weren't marketing to motivated sellers. As one smarter than me once said, "If you aren't embarrassed by your offer, you are probably paying too much". For quick analysis, you only need to determine two things: 1) The ARV, and 2) How much repairs does it need? Then you could pay full retail (ARV) if you wanted to live there, but you will need more than a 10% discount if you are looking to flip, and more than that if you are looking to Wholesale this one. Whoelsale buyers are all at 70% of ARV and sometimes less, in our experience.