Jordan, after you spend a day working one of those tables you get back to us on how charming and polite you stayed while fending off vultures who try to buy things before you have a chance to put it out, slobs who throw all your merchandise around, and especially those who think that because you are standing behind the table that you know every single thing that your group donated and can tell them exactly where they can find it and how much and can they have it for less?
When I've worked the booths, I made sure that everything was priced and labeled BEFORE it was brought to the table (live and learn!), but unless you've done it before, it's a HUGE and wearying task. Remember that EVERYONE working there is giving up a valuable morning off so that they can help out- they're not professional flea-marketers. To show up and lug big boxes of junk through Times Square at 9am and then have the vultures trying to buy things before you are ready to sell is highly annoying. There's a start time for a reason, and just because you are there early doesn't mean everyone is ready for you.
That said, no, they shouldn't have snapped at you. But try to understand why they did- because if you were so eager to buy something, then maybe they could raise the price... it IS for charity, after all, and we always try to get the most money we can AND get rid of everything we have. This is why prices start high and are marked down during the day.
I have loved working the booths and will do it again when I can- but it's a damn hard job (especially when you have to leave to go work a matinee, then come back to clean up) and the people who are giving up their time to help you find that flop-show windowcard deserve a break.
"What- and quit show business?" - the guy shoveling elephant shit at the circus.