How would you group people who bought tickets through the site?

[socceronly]

If we were selling tickets through our site, at only 1 per member, what ideas do you have for grouping those people.

Tickets will be distributed via Ticketmaster, so we can export the data and sort in an excel sheet.  

The question is what is the best way to get that field populated that we sort on?

Let them decide and it is up to them to enter correctly in a text field?

Any other ideas?