The only people that are allowed to open your bag is security. Ticket agents are not allowed to open your bag.
Even if your quote may be true, ticket agents can still ask you
to open your bag...if you refuse, they can refuse to take your bag...I'd suggest either rent a board where your going or be ready to pony-up some cash at the ticket counter.
Read the airline's policy regarding damage to sporting equipment, which basically states that the airline is not responsible to any damage to sporting equipment unless it is packed in a hard-shell case. So even if you pay the extra charge, if your board gets damaged...its your loss.
So it may be cheaper and less stressful to just rent at your destination.