Pretty sure the "Supply /Demand" concept would work the opposite of that (more stuff would mean lower price, v.v. ). From the very little I know, it might even reset (twice a MC day, and /or once instead only each 20 min's. of that MC day cycle), and I'd check the MC Wiki.
The "Hero of the Village" Effect is likely to get you a better /the best price, even aside-from selling a-lot of something, and then attempting to buy it back (I mean, if that combo. is possible). But of course it's dangerous to get it, after all it's the Village & Pillage.