What is the ruling on buying a commodity from individuals, then presenting it to an entity that buys it after examination and price determination, then agreeing with the original seller on his share after receiving the price from the purchasing entity, or after the entity's direct acceptance, or before presenting the commodity to it?

The correct method is to purchase the item from its owner for an immediate or deferred price, so that you do not sell what you do not own and profit from what you do not guarantee. After purchasing, you can stipulate for yourself an option for three days, and present the item to the concerned party. If they accept it, you sell it to them; otherwise, you have the right to return the item to the seller by virtue of the stipulated option. If the option belongs solely to the buyer, then his disposal of the sold item becomes effective, and his option is nullified.