Okay, I had to try it twice to belive it but, you can get free furniture and, actually get paid to move in and out.

First build an apartment, funish it with the best of everything, money is no object. now, once you've zoned it and are at the neighborhhood turn testing cheats on (ctrl+shift+c then type boolprop testingcheatsenabled true)

Chose a family, or create one and move them into the apartment you built and funished. Shift+click the door and rent funished apartment. Save as you exit the lot, move the family back to the bin from the neighborhood screen.

Now move them back in to the same lot and again rent the apartment funished. Repeat the move in, move out as often as you want. Each time your family will get the value of the furnishings that would normally be deleted when you rent but, the furniture stays in the apartment.

Example: Single sim moved in and rented furnished - funds 18,883. Move out then in again 98,078 and again, 177,273. Same apartment and always furnished.