Auctria requires each bidder has a bidder# associated with them.
Multiple bidders can share a bidder#, in this case they are said to be linked. See Sharing Bidder Numbers for more details.
The system will automatically assign bidder#'s when people buy tickets, or register, online. This can cause problems for events that want to hand out bidder#'s at check-in. In this case, the best approach is to set the system to assign a very high bidder# automatically. This setting can be found on the Auction Details page in the SUMMARY tab's "Advanced" panel.
If all the auto-assigned bidder#'s are at, for example, 18000+ then you can easily reassign the numbers at check-in using the Check in Bidders page. You can also tell, at a glance, if bidders have checked-in by their number.
A related approach would be to renumber all bidders using the Renumber Bidders page to have a high bidder# before check-in, and then change the bidder numbers as bidders check-in at the event.