It all depends on various parameters like price, demographics, investment strategy, goal etc.,.  

He could pretend to be another random person checking out the house, but I think buyers don't want to offend, so they don't give honest feedback to the seller.Yeah I guess it really just depends on your market, demographic of buyers, etc.

Use demographics to determine if the area is a good investment area. 

Demography is definitely one of main factors, so we are talking about two main demographics for apartment complex : Millennials and baby-boomers.According to the research,Millennials,young professionals, given their financial profile and lifestyle preference, will prefer small units in walkable urban neighborhood.

I didn't just put demographics and cap-rates into a spreadsheet and *poof* it spit out the Top 5 markets!  

@Clint Galliano, the reason that number varies (and most other number too - maintenance; capital expenditure; tax; utilities; insurance; property management...) is because every County has different demographics, which can highly affect the correct analysis between different properties.Sorry about the non-specific answer. 

@Corey Smith Southeast King county is a pretty specific demographic.

Thanks for the great tip @Rob Myers , I'm going to have to do a little more reading to see what opportunities/challenges the military demographic presents as I'm woefully under informed.  

I'm always studying different markets and have put together a matrix comparing the ROI's and the economic/demographic of some of the top markets.

There is a lot of variation in this depending on the building type, age of the components, class of building, demographic, amenities, etc.