Not anymore - as much as some cargo operators would love to earn a few extra bucks/quid/euro/whatever to defray the exploding fuel costs by selling off these available seats, 9/11 changed all that. Unlike passenger planes, main deck cargo hold and cockpit are accessible during flight. So, for security reasons, no more passengers, only folk who need to be there for a good reason, like additional pilots, engineers, loadmasters, grooms. One of the setbacks of freighter aircraft - no pretty flight attendants serving coffee to the crew. If the two guys in the front seats get very lucky, they might cajole a grumpy mechanic into getting them a cup, which he probably spat into before bringing it up front cuz they gave 'im grief bout them DMI stickers
