Siman 186

One who takes vessels from a craftsman's house or from a shop to send them as a gift to his father-in-law's house or to another person, and he fixed a price with him, but stipulated that when they receive them there he will pay him the price he fixed, and if they do not receive them "I will give you a small fee according to the benefit I derive from the recipient seeing that I desire to give him a gift," and the object was lost to him by an unavoidable accident on his way there, he is liable. For since he fixed a price with the seller and took them, they are considered purchased in his hand until he knows that they will not receive them from him. And when they did not receive them from him and he was bringing them back to the seller and they were lost by an unavoidable accident, he is exempt; but if they were stolen or lost, he is liable, for his law is like a shomer sachar, because for the benefit he has in showing them in his friend's house, he has the law of a renter, whose law is like a shomer sachar.

If he took them in order to sell them and fixed the price with him, and he will profit whatever he takes more, and he said to him: "If I sell them in such-and-such a place or by such-and-such a time, I will give you the money I fixed with you, and if I do not sell them, I will return them to you," and they were lost to an accident either on the way there or on the way back, he is liable to pay. It is not similar to the previous law where he is exempt on the return, for here "return" is not applicable, since if a buyer happened upon him during his return, he would have sold to him; it turns out that until he returned them, his status is that of a buyer and he is liable for accidents. And some say that this is only in a case of an item that has many buyers, such that he could sell them immediately at the price he takes from this person, but rather he is doing him a favor so that he may profit from this; thus it turns out that all the benefit is the buyer's, for the seller would have found many buyers. But without this, he is only liable for theft and loss like the law of a broker, since the benefit belongs to both of them, and upon return, some say he is only like a shomer chinam [Netivot HaMishpat]. And so too, if he fixed a price for him and said to him: "Whatever I take more, we shall divide between the two of us," even in an item that has many buyers, he is not liable for accidents. And from this we have learned regarding the large merchants who give merchandise to the small merchants so they may profit from them: if the primary favor is for the small ones and the large ones are not waiting for the proceeds, and their entire intention is to do a favor for the small ones, the small ones are liable for accidents. And if not, they have only the status of shomrei sachar. And if Reuven had an object to sell, and Shimon came and said to him: "I wish to serve you; give me the object and I will sell it for the sum you say," and Reuven said to him: "Sell it for such-and-such, and the remainder shall be yours," even though Shimon remained silent, he is a shomer sachar and liable for theft and loss. And Reuven is unable to take the remainder beyond what he fixed, for in this, silence is like admission, and they both agreed and accepted; thus it turns out that the benefit of both of them is in this, and therefore his law is like a shomer sachar and not like a shoel, even if there are many buyers for it, since initially he accepted it for the benefit of Reuven [as mentioned above from the Beit Yosef, see there]. And if Reuven did not say "the remainder shall be yours" but only "sell it for me for such-and-such" and Shimon remained silent, his law is not like a shomer sachar and the remainder belongs to Reuven, as written in siman 185 [ibid.]. And some say that even in this case the remainder belongs to Shimon, since he said to him "I will sell it for the sum you say," it is as if he said to him "the remainder is mine," and his law is like a shomer sachar [Bach].