Lower the town tax and plots cost
and
Higher the price for selling

Item/sell/buy

Iron, 2 / 5 (For one ingot)
Gold, 4 / 8 (For one ingot)
Diamond, 8 / 15 (For one)
RedStone, 2 / 6 (For 16)
Lapiz, 3 / 6 (For 16)
Coal, 2 / 4 (For 16)

Log, 6 / 10 (A Stack)
Wood, 3 / 5 (A Stack)
Cobble, 2 / 5 (A Stack)
Stone, 4 / 8 (A Stack)
Stone Brick, 6 / 10 (A Stack)