And @Brandon Diaz, is right: certain markets/areas don't fluctuate as much.  

SEO, fluctuating markets shady contractors, SEO, People, SEO!!

My wife works basically a waitressing job so her pay fluctuates way too much but she cannot find any other work down here.

I think demand for these locations will overcome market fluctuation in the long run.In Lynn stay away from the Lynn commons in the center of the city. 

I can't control a stock or mutual fund, so many things can make it fluctuate-- and you just have to go along for the ride.Your wife is probably thinking of the notorious 3AM phone call, so maybe push the idea of a property manager so it'd be just as passive as a mutual fund. 

May seem crazy because of the fluctuating cost of materials but the locations are in high demand for each and the projected returns are too good to pass up on the opportunity.

What about fluctuations from investments from cash flow over time earned from that project or original investment, you'll find yourself in what might seem to be an endless loop.

If HELOC’s have a interest rate that adjusts/fluctuates/variable based on market conditions, why would anyone take out a HELOC compared to a regular home equity loan?

@Allan Smith That makes sense, I was thinking about the fluctuating rates of a HELOC.

It may fluctuate with markets but it does not depreciate.