But on the other hand, it happens that the plentiful supply of necessaries lowers their price. This Seneca, in the 15th chapter of his sixth book on benefits, proves by many instances, which he concludes with the following observation, "the price of every thing must be regulated by the market, and notwithstanding all your praises, it is worth nothing more than it can be sold for." To which we may add the authority of Paulus the Lawyer, who says, the prices of things do not depend upon the humours and interest of individuals, but upon common estimation, that is, as he explains himself elsewhere, according to the worth which they are of to all. Hence it is that things are valued in proportion to what is usually offered or given for them, a rule admitting of great variation and latitude, except in certain cases, where the law has fixed a standard price. In the common price of articles, the labour and expence of the merchant in procuring them is taken into the account, and the sudden changes so frequent in all markets depend upon the number of buyers, whether it be great or small, and upon the money and marketable commodities, whether they be plentiful or scarce. There may indeed be casualties, owing to which a thing may be lawfully bought or sold above or below the market price. Thus for instance, a thing by being damaged may have lost its original or common value, or that, which otherwise would not have been disposed of, may be bought or sold from some particular liking or aversion. All these circumstances ought to be made known to the contracting parties. Regard too should be had to the loss or gain arising from delay or promptness of payment. XV. In buying and selling we must observe, that the bargain is completed from the very moment of the contract, even without delivery, and that is the most simple way of dealing. Thus Seneca says, that a sale is a transfer of one's right and property in a thing to another, which is done in all exchanges. But if it be settled that the property shall not be transferred immediately, still the seller will be bound to convey it at the stated period, taking in the mean time all the profits and losses. Whereas the completion of bargain and sale, by giving the purchaser a right of possession and ejectment, and conveying to him the hazard with all the profits of the property, even before it is transferred, are regulations of the civil law not universally observed. Indeed some legislators have made the seller answerable for all accidents and damages, till the actual delivery of possession is made, as Theophrastus has observed in a passage in Stobaeus, under the title of laws, where the reader will find many customs, relating to the formalities of sale, to earnest, to repentance of a bargain, very different from the rules of the Roman law. And among the Rhodians, Dion Prusaeensis informs us that all sales and contracts were confirmed by being entered in a public register.