We show at trade shows, although of a different sort, and for the price we pay per square metre, I wouldn't imagine belittling the competition or deciding a potential buyer wasn't worth speaking to - we're there to make money after all.
On the subject of belittling the competition, we've had one designer who we considered competition, buy from us to put prominently in his own shop, A lot of shops who've bought from us, have our products on the shelf along side our competitors products - they compliment each other, and help the eco system of the shop work, if we slag off the competition (who they like) they wouldn't buy from us.
Equally, there has to be some ignoring of people coming round, as unfortunately not everyone coming round is an actual buyer - effectively they are spies, trying to copy your work, be they another designer, or a student (if you do talk to them, they ask very pointed questions about the work and how it's done, rather than how many units they have to buy)- name badges come in useful here to try and work out who people are before you talk to them, but you have to be subtle in trying to spot names and companies on the badges whilst they are walking over. Some hide their badges, and this maybe because they're spying, but bigger buyers do this too, so you don't get flustered and talk to them like any other buyer - had this happen at our first show, and towards the end of the conversation he revealed he was lighting buyer for John Lewis!
There is also the decision of working out who is worth talking to, as you can only talk to one person at time, so on a busy day you can end up talking to someone for an hour, whilst no one else can talk to you, in the hope that they put in an order to be worth the time of you not being able to take other orders (had this happened at our last show) and thankfully some buyers came back later, or got in touch after the show.