Clients can maintain one or more items in their showroom for public viewing. While a client's store does not handle e-commerce (i.e. visitors cannot buy an item), they can get all relevant product information including pricing, attributes, descriptions, availability, images and contact information.
Of course the Linear system does feature a full-functioning shopping cart solution, but this intended for the primary operator of the software (i.e. you). You could include your client's products in the Site store, but the issue of fulfillment may be a concern if a shopper were buying product form multiple vendors.
Keep in mind, the Linear system is targeted to local Web sites where the typical Web visitor probably lives within 10 miles - they would prefer to drive and purchase a product rather than waiting and paying for shipping and delivery.