Moving into a mansion for free does not exempt you from the weekly bills . Expensive houses have high tax rates; ensure your Sims have a high-paying job or use money cheats later to keep the lights on.
Open the console again ( Ctrl + Shift + C ) and type freerealestate . sims 3 buy any house cheat
Press Enter. You will notice that houses previously "greyed out" due to high costs are now selectable. Alternative: The "Motherlode" Method Moving into a mansion for free does not