Those that are durable have an expected life-time and an age using which we can calculate its depreciation. Each item in the system has an owner. This owner can be a shopkeeper or an ordinary person. Both of them can sell the items that they own. There are different kinds of shops.
Agents have some commonsense knowledge about where the ordinary items of daily life are sold.
The values of these items are also within the commonsense knowledge of agents. If an agent has enough money and knows where to buy the item, he can buy it. The ownership of items depends on the kind of items. If an item is movable, the owner holds the item physically. If an item is real estate, there are documents about the item and the person who holds these documents owns the item.