In the bay area instance, the average median income household cannot afford to buy a home.

So maybe in your case, you look for folks with 3 beds that have a household income  X% above the average of the area.

Just put in an offer for around 715k on a building in a lower income area in Chandler AZ, but surrounded by good neighborhoods with great schools, as well as higher income areas This particular neighborhood's median household income is around 30k whereas surrounding neighborhoods are 60k-85k.

You can also look under the Economy heading and see household incomes, unemployment rates and job growth for the area which can all influence rentals for that area.

Significant in absolute numbers when the country has 122 million households. 

In markets where the median home price / median household income is very high, a higher interest rates will have much more of impact in housing prices compared to where the ratio is very low (lower than 3), thus the housing in the area will be less impacted.

I've advertised many household items on craigslist and most have sold within the first day of posting.

Coney Island and Brownsville neighborhoods have median household incomes of $9500 in 2013.

Remember that an electrician does make good money after his apprentanceship but it is seasonal work so your household income may fluctuate throughout the year.

The overall vacancy rate is not atrocious, 11% which tells you they rent fast for right price.You are in a low income area, median household is barely $36k/yr. 98% of the local residents didn't go to College, so you get an idea of the wages.