Penalize players who adjust their prices too frequently

[Mavlok]

I intentionally don't buy for the lowest price if I notice they've undercutted by a ridiculously low amount, like 1 gil. However, I notice that many players do reward those specific undercutters.

Redesigning the tax from selling so that rather than losing 5% to tax after the item is sold, to maybe 3% in tax after the item is sold, but 2% when the item is actually posted, would help a lot to prevent the silly undercuts.

So you'd prefer a 10000g*99 deal over a 9999g*99 one just so you can teach a lesson to... whom? Your own pocket? This doesn't even make sense. Your notion of "silly undercuts" is silly and childish. The only law is supply and demand. If they manage to drive you away as a seller with undercuts, it's their gain.