Hope for the best but plan for the worst.  80% is probably more realistic. 

Its usually best case.When you start out, think of 3 different scenarios for each place you analyze:1) What is the BEST case scenario (rents for top dollar, minimal repairs, all is fine)2) What is the WORST case scenario (Big things go wrong, how long will it take to recover it all and be profitable again, etc.)3) What's an AVERAGE case scenario (somewhere in the middle)Run these %'s and you'll quickly get a sense of what's comfortable and what's not.

Yesterday , we had snow , sleet wind and rain . So my second phone call in the morning was from a tenant . "We have no water "    ( House is on a well )   . So I go over and check the breaker , then the pressure switc...

This does not give you confidence he is good, only eliminates the absolute worst cases.If you want confidence - hire one of the accountants who contribute to this forum.

I actually had to bring people up from NYC to work because I couldn't find quality contractors willing to do the work, what was worst was finding an Hvac contractor.   

Next, "helping people out" is probably the worst thing you can do from a business standpoint.

They are drudging up the worst of the worst bottom of the barrel properties, which tend to to be really low end properties.

And that isn't the worst part.

Worst case scenario, should you decide to continue with this deal, you put your things in storage and stay in a hotel until closing.The current owner probably has to evict the tenant through the courts, and that could take a long time.

People don't stop sending their children to school.If anyone is going to allow the worst possible case scenario to convince them to not invest in real estate, well, they probably didn't really want to be a real estate investor in the first place.Maybe the fact is your wife really doesn't care to be a real estate investor.