What is the name of the local aquarists society hosting the event.
You will have an auctioneer who will describe the lot and take bids from the floor, bids will usually go up in small amounts (10-50p) until they reach a certain point and then they will increase in monetary value until the last person bidding wins the auction lot. From my involvement in a great many events in the past I would expect to see fish, breeders personal stock surplus, livefood, tanks and equipment and other aquatic odds and ends. Anything could crop up, a really good fish auction is not to be missed, especially if it's within walking distance.
I too was a little apprehensive walking into my first auction...once you get the hang of it (no-one is out to judge or poke fun at others) then you will be bidding like a pro. Set yourself a maximum and dont go beyond that is unless you really want or need that particular fish or item, then who knows what it will fetch...LOL
A good auction is the place to be, you may see rare fish that don't reach LFS/dealers tanks , there is always something that sparks a real interest.
Try to get to know the local club representatives, who they are, and maybe join the club, they could do with your support especially in this day and age.
I would always advocate joining your local club, you wont regret it. The knowledge base & comaradarie is second to none whereby a better insight and understanding of fishkeeping can be gained by doing so.
Enjoy your day out
Regards
C