Please take a look at the awesome feature OLX.ph launched:
A calculator for estimating how much the stuff you have at home can be sold.
http://corporate.olx.ph/yamancalculator/
I love this because
Inspire users what can be sold.
Estimate how much it can be sold.
Looks very simple (I think it's hard-coded and not really sophisticated analysis of prices on the site).
I had this idea a couple of weeks ago :)