Is it permissible for the buyer to ask the seller to reduce prices or the total invoice after the final agreement and payment of a down payment, due to discovering an increase in the prices of some items?

The buyer is obligated to pay the agreed-upon price if the sale contract has been concluded, even if the price exceeds the market value. However, if the buyer requests to be exempted from part of the price and the seller willingly agrees, there is no harm in that.