Well your wanted ad just doesnt have a price to add or subtract thats all
As noted the only way an amount can be subtracted is to hit RELIST
However for RELIST to be shown SOLD has to have been clicked which sets status higher than 0
Thus SOLD adds and RELIST subtracts which is the tit for tat I spoke of.
In all my testing thus far everything works as expected. I have posted under several dummy acounts on my test install different ads with different prices and hit sold and relist many times and checked and the stats show correctly