I like to watch the event calendar on this forum for upcoming shows. Sometimes there is one near wherever I will be traveling. I don't always go to coin expos, but when I do, I take lots of cash with me. Sometimes I find nothing, and sometimes I find something so sweet it pays for all of my traveling. The trick is being ready with lots of cash. Cash is power. When the dealers find out you have cash, they want to meet you, haha.
Most of the best deals happen at the beginning of the show, or just before it starts when all the dealers make deals with each other. Those "dealer only" times are one good reason to officially rent a table at the expo, and only use it get access to early deals.
The next best time to buy is when you see a dealer starting to pack up his coins, to go home. Very often I will see a coin I want, but the dealer is asking too much money for it. Sometimes I find coins I might buy if the price is right, but I don't want to make a strong offer for it. If I pull out my cash and pretend to start counting it right in front of him while he's packing, I can wait a moment and then make an offer on some of the coins I wanted. If he has more than one coin, I can make an offer on all of them. I end up getting "dealer only" prices at the end of the show, in a good fraction of my attempts to haggle a deal at the end. Sometimes the dealer did not do very well at the show, and he needs cash. In that case, he might be willing to take a loss instead of going home without the big wad of cash I'm waving around.
I'm sure other people have secret bargaining tricks of their own.
