What is the ppsqft for new comparable quality construction selling for and do not pay more than 65% of this... my 2 sense.  

He is a savvy guy and knows what price points would make for a workable flip price compared to a workable rental price.  

If you're going to flip the property, then the attractiveness of the home would come more into play, as well as it's features compared to the competition of other homes in the area (as you mentioned, lack of curb appeal, lake frontage, size, inconvenient commute).

Cap rates compare NOI/Sales price and that's an evaluation of one prospect against another - - so comps are required.My buy&hold decision was based on cash-flow and the cash/cash return. 

If you can go visit some open houses within your neighborhood so you can see how they compare to your home and what you are up against.

I paid too much for my primary compared to the other properties around me.

I think your confusing what agents and brokers do compared to investing.  

Single tenant retail is a breeze compared to office buildings. 

You can often see how much care/attention/time an owner gives a property based on how it's maintained and who lives there compared to other like buildings in the neighborhood. 

Comparing situations where the home is badly burned or vandalized and someone buys it for a dollar, how much work is too much work for a first deal?