In this attic there were 10 vacuum cleaners, 7 TVs, 8 mattresses, 8-10 microwaves, mountains of clothes, several bowling balls, pots and pans for 10 housholds, and several tons of other junk collected from at least 20 years of tenants.

Cash in the mattress?

If a paid off house and or mattress money makes him happy, he should do that!

I have (although do not currently) managed buildings in two of the absolute worst neighborhoods on the island- where toddlers play on old discarded mattresses laying by the roadside in broken glass- but still applied the same criteria when obtaining new tenants for these properties.

It's been a PITA sleeping on an air mattress and working instead of playing golf every day, but maybe this time it stays sold.Yay me!

Our landscaper called us Saturday and said the kitchen table and master bedroom mattress was missing.

Then, as in the case with my company, we offer a Zero Down program where you put nothing down, and you can save your cash for other investments, or to sock into the mattress for a rainy day.While many people might disagree with me, I come from the school that the real wealth is created off the tenants paying off your asset and the long term equity that a home provides, any cash flow is just much loved icing on the cake, and just makes it that much more attractive!

All you're doing is transferring your cash from your bank account to one of the mattresses of the property...and rendering that cash dead.You are NOT saving interest charges, since you were never paying the interest in the first place (remember the tenant?). 

The apartment was not cleaned, she left a bunch of her stuff as well (furniture, mattress). 

Well, as a seasoned investor I wouldn't plan on a 1031 and then post on BP asking how to do it :)Put this money under the mattress until you figure out what to do with it.