The prohibition on smoking set forth in Section 6-35 and 6-37 shall not apply to a public place or place of employment of a tobacco dealer that permits customers to sample tobacco products on the premises of the tobacco dealer, provided that smoke generated by smoking on the premises of the tobacco dealer does not infiltrate any other enclosed public place or place of employment. For purposes of this exemption, a tobacco dealer is a retailer whose principal business is the sale at retail of tobacco and tobacco-related products.