Yes, I'm a lender, but we have an arm that's been investing for close to 20 years now. We've never used percentage-based criteria, like the 70% Rule, for purchases. Simply put, we start off with the As Repaired/Completed Value (ARV), then subtract from that number a reasonable profit, the rehab cost (scope of work), which we've gotten good at, a contingency reserve for any "unexpecteds", our cost of capital/carrying costs (interest and costs of the leverage used), and our costs/fees on the buy and sell sides of a flip. That gives us our "strike price", which is the highest amount we're willing to go to purchase a property. I've found that those percentage-based rules have mathematical flaws in them. MInd you, we've gotten really good at our scopes of work and we have one of our GCs go through the property with us to give us our scopes of work. We've also advised this method to our investor clients that borrow from us. I will die on the hill that the 70% Rule is flawed. We avoid lending to folks that don't really have their math/numbers together. I hope that helps you.
On another note, just because your offer isn't close, as you said in your narrative, doesn't mean you're wrong with your offer price. There are a lot of idiots out there overpaying for deals right now...well...that always seems to be the case. If you get your system and modeling down and follow what I mentioned above with respect to coming up with your strike price/offer price, you shouldn't look back if someone overpays for the property. It's just a math problem and if you've done the work up front you shouldn't second-guess yourself. There are many, many investors that don't do their math up front.