[ChristianGeek]

What if you provide a discount code in the ad that’s unique to the ad? Subsequent ads have slight lower discounts so there’s an incentive to use the code from the first ad they saw.

[petercooper]

Discount codes was one method used, the only problem was that at the $1000+ ticket level, it's often another department buying the tickets and they frequently don't bother to use the codes :-D

[icebraining]

Might work for some people, but the probability that I would even remember the first ad had a code - let alone the exact string - is minuscule.

[lozenge]

Not being able to find a discount you saw can be pretty frustrating. Less important in this case as employers often pay for these conferences.