Good advice by all, and without going over the saliant points posted one by one, I'll throw in these .2 cents worth.
Having worked both sides of the table, I think this tack works best....
Know your knives, know what ya want, know what that "special" knife is valued at in the current market, know what you can rationalize spending on that day, and most importantly....be polite.
If you're really interested, smile, be polite, wait your turn, and speak clearly about what you'd like to do.
If ya want the knife but don't have the money that day, take a card, leave a card. Make personal notes on the back of the card you take or leave. Let the seller know when you'll have the money.
Smile, laugh, have fun, and treat the folks you're dealing with the way you'd want to be treated. The same goes for the knives.
Ask if you may see it, be careful when ya pick it up, be even more careful when ya put it back down.
Gaaawwwddd, we had this guy come by twice, pick up some expensive/rare knives, then get bored and drop them back on the table.
After the second time I asked Edna to watch the table, walked up behind the guy, took him by the elbow, hissed in his ear, and spun him around to face one very, very pissed off...me. He was shocked, apologized and all, but damn, I was seeing red!
So, a smile goes a long way. Listen, don't just talk, and be polite! If ya had to script the perfect interaction, make your interaction match that script, and be polite.
If a seller is rude, walk away, but be polite.
If ya network, make friends, enjoy the collecting, and know what ya want, you'll have more fun than you can possibly imagine.
My .2 cents worth.
Mel
"Buy Quality and Only Cry Once"