Most of the idea sounds good to me, at least with SOLD being obvious, it prevents wasted time when perusing ads and could simplify searching for something.
I can see an advantage in leaving the item description and price after the sale to help evaluate the true value on future similar items.
I can't see why a "reason for selling" is relevant. If it wasn't as advertised, useless crap, wrong colour, unwanted gift etc. is basically no interest to me when I am buying something, and if I'm selling, and if the item didn't work to expectations, the last thing I would tell any prospective purchaser is that it wasn't worth keeping. It just seems to open up a negativity to an item.
Cheers
Ian