Finally he found a floor mat that had migrated over the air return vent on the floor. 

You can make minor adjustments based on the type of appliances (dishwasher, clothes washer and dryer, air conditioning, etc.) and the size of the rental.

I looked at few houses in Bell Air community but I found it difficult to even break even with mortgage.

This would not be my first choice unless you have an air-tight exit strategy that does not rely on a bunch of "maybe's".

I downsized the heating and air system but added a 2nd, separate system. 

The roof was replaced this year and the Central Heat and Air unit was replaced within the last 3 years. 

Renters do not change out air filters!  

Some electrical is involved to add light to bedroom and some work to add air register.

They are as in-expensive as any competing importer and nobody matches their specs in the price range.The plywood is good hard plywood not the typical soft import plywood.Their products meet the California Air Resources Board Phase 2 requirements for formaldehyde emossions which is a huge issue with import plywood.Their finish is a UV cured, water based Benjamin Moore stain just like the American product.  

Chances are the tenant just wants more air flow through the place.