Something I've learnt as both a visitor/buyer and as a vendor is that there are tons of people ready to bust down the doors to run around and buy what they want before the crowds come. I've both bought like that and sold like that. These days, I like to browse the local reptile association websites and see who is selling what at the expos and if there's something very special at a good price then I'll reserve it, otherwise I like to look, compare and barter a little before buying. Sometimes if a particular morph is over represented that day, you can find that at the end of the day there will be a lot left at cut prices...I bet those butters didn't start so cheap!
It's heart breaking selling hatchings at ½ what you wanted for them in the first place but I have a friend who was slashing his prices to 15% of the original just because he didn't want to take anything home at the end of the day. I cut my prices but I don't sell too cheap. I think knocking 20% off with 2 hours to go is fine and buy one, get one free is OK towards the end of an expo.