How do seasoned investors know what a deal is with no inspection.

[Nick Stille]

So I'm just getting into this real estate endeavor, looking for my first flip. I hear people, like on the BP podcast for example, say they saw a "deal on the MLS and had to jump on it, making an offer that very morning." I'm assuming that they couldn't have possibly visited the exterior of the house, let alone the interior. I'm not quite sure how they can so accurately assess what is a deal without settings foot on the property. I'm sure some of this comes from experience, but is there a metric that people use? For example, lets say you have a $100k house. Using the 70% rule, you should buy it for $70k - rehab costs. But how do you accurate compute the number so quickly on a property you have simply heard about and never visited? Would you assume a percentage, say 20%, for rehab, and therefore buy it for $70k - $20k = $50k? Or is there a cost per square footage that people use to give themselves a rough rehab cost? When making quick offers on properties like this, do they roughly compute the numbers, come up with an offer, then later go and inspect the houes with an inspection clause in the offer, so they can back out if the inspection turns up anything more than a typical inspection? Any information would be helpful. I'm still trying to get a handle on how to find my first good deal. It's a bit nerve racking, so I'm just curious how experienced investors calculate values of deals so fast. Maybe they are setting foot on every property before making an offer, so correct me if I'm wrong. Thanks BP community!