Easy solution - Ticketer should accept tickets back.
Ticket supplier (ie venues and agencies) should buy tickets back, maybe minus an admin fee until the physical ticket is mailed out.
The fact they don't helps create the secondary market, most times I've been at an allegely sold out show or event I've seen empty seats. No doubt something cropped up and the original purchaser could
not go, but as no-one accept's tickets back they can't easily be sold on.
Theres the issue of not filling a venue to capacity and people buying more tickets and returning them, hence the need for an admin fee (maybe like holiday booking a sliding scale say 10% a month before to no refund if you cancel the day before) to stop abuse and there is a counterfeiting angle but for events that only send the tickets out a few weeks in advance theres really no reason why they can't accept a return, make a refund and resell it before the ticket is sent out.
The ticket agency would get the admin fee, the event would still sell loads, and the touts and the resale website potentially would get less traffic.