I am also wondering what sort of Up-Sales I can try , like offering a trial lesson at a discount if the person is hooked after the scenic flight, Or Perhaps a Certificate on completion. All idea's welcomed.
Offer a time-limited (3 months?) discount for the 1st (easy) lesson in the regular training methodology (which is typically a get-to-know lesson from the left seat anyway).
Certification of Completion - yes, preferably with the photo of the airfield or aircraft on it, and the participant's name.
Another idea is that you give small value time-limited vouchers for the participants, that can only be used for bringing someone else for a similar flight (scenic or training). So if they bring in a friend, or someone else in their family (not present on any events before), those will get the small symbolic discount from the list price. People love to share experiences, so use this to expand your reach and number of visitors
Memorabilia - if you have some obsolete stuff in your hangars, you might bring them forward onto a table.= for dispaly. If there is someone who can tel good stories about no longer functioning flight instrument (which aircraft it was in, who flew it, what adventures this a/c had), there is a chance that 1 or 2 guests would like to take them home a souvenirs
just make sure the paperwork is done correctly, so it doesn't end up in another airplane via the black market.