This year has been a giant pain in the A in getting tickets. I had a couple ideas that I thought I would share that I think would make things easier.
1) Let people who come to the con sign up for the following year (pay in advance). They can only get 1 badge. You can cut or mark their badge in a way so that you know they have already redeemed their badge for the following years badge. By limiting these purchases to one per person, it will be less likely that the person will sell the badge on eBay. It also guarantees they can come and enjoy it again. Also, you can even be more extreme about it and only 3 day holders can get 3 day badges. If you have Fri and Sat badges then you can get Fri and Sat for the following year (You would only have to buy a Sunday badge when they go on sale to the public afterwards). If you have Fri-Sun individually you can get all 3 marked up and get in on a 3 day.
2) Get rid of the 3 day discount and flat fee all the days. There is a profit potential that people can use cause of the savings. You can even make it that if someone attends all 3 days they get a PAX shirt and some goodies in the mail with their badge as a thank you for attending all 3 days. With there being no savings in 3 days hopefully more people will opt out of trying to eBay the tickets. For those that would like to attend 1 or 2 days, they have the option to get said "goodie bag" for a small fee of $20 or whatever.
You could even combine both options which I would be fine with