I won't be buying much, if anything at the Expo. I find the notion of paying for overpriced plastic as appealing as buying an ex girlfriend more lingerie she'll wear for someone else, again.
So I'll tell you how I haggle.
Know what you want and how much it costs. Then approach the seller with how much you want to pay in your hand 20% less is usually fair (take into account their mark-up) and an extra £5 or £10 in your pocket. Smile, and be geniunely interested in what you're buying, make it sound like "it's going to a good home". Ask how much it is, or if it's a lot of things, ask how much they are altogether. Then what deal the seller can do for you, this is important, make it sound like he WILL do you a deal; You're not asking for a deal, you're asking him the price of a deal he hasn't agreed to. As soon as he tells you a price, BAM there's your agreement he'll do a deal. With the money you have, say "I've got this much £, and that's me done for today" (Again, assume he'll do it at that price). If you're lucky, you'll have closed the deal there. If they go "Mmmmmm.. I can't let it go for that price" fumble about and get out your emergency £5 or £10 and then go "Okay I really want these" and see if you close it. If you STILL don't get that deal, walk away. You tried, there's no point in paying full price for that now.
Good lines to use:
"It'll save you packing it away and the petrol needed to take it back with you unsold"
"That stall over there sells it cheaper, but it's not as nice as yours"
"What's your best price for me to take them all right now?"
"I'm not coming back to hassle you for the offer if I turn it down, I'll buy it or walk away, so what can you do for me right now?"
"You'd totally make my weekend, and I'll be the only one asking for it"
Should save you buggerlugs some pocky money.