They also do not have to deal directly with the buyer. Most auctions sell 'as is' and when the hammer falls, the animal is the property of the buyer at that instant. All contracts and guarantees are as called in the ring and are between the buyer and seller. The auction house provides the service of a facility of where buyer can purchase an animal at a called price if it is accepted by the buyer. No more, no less.
Some auctions prefer to take consignments as called in ahead of time, and in that order.
Others number the animals as they are received on site. Some auctions sell the animals in the order received regardless of species and others group similar species and sell each of those in order received. Many, many reputable sellers use the exotic sales as the major means to sell their quality animals. It is possible to get some terrific buys at an auction, but then again you could get home with a pig in a poke. Unless the seller guarantees the animal in the ring, you are buying it 'as is'.