As I said in another of your threads I would stop with the LOI on residential properties and use a standard PA - if these are investors in single family homes they may have never heard of a LOI.
How do you act? You don't - be yourself. Acting will only get you in trouble. Sure fake it till you make it but that is pretend you know what your doing when you don't - but be yourself.
Beat up homes that are 70 years old may or may not be good - way to little info to know. Nice neighborhood? Is it a place where people live and rent? Really depends on the home / area.
Investors can be a tough crowd - most think what they know is fact and your not going to convince them otherwise. If they think the home is worth 100K you can show them stats till YOUR blue in the face - they won't budge.
But try it - after you do it 2-3 times you will start to find what works.