I’m not sure if you’ve set up your booth yet, but yes, you are forced to put down a price. If you’re not interested in swapping the piece for cash, but in trade, nothing stops you from putting down a ridiculous high price while in the description box writing that you’re more interested in trade.
However, keep in mind that wanting to do a trade during Comic Art Live and theoretically not listing a realistic selling price defeats the purpose and the spirit of what I think Bill is trying to do here. I, for one, as a shopper, don’t want to go to a con where 2/3 of everything is listed as $500,000/“Trade Only”. If you have other things you’re willing to sell for cash, maybe in your booth description you can write that you have X to trade for Y, and to “write me for details.” Your booth is also linked up your comic art classifieds/MyComicArtShop/For Sale Gallery, so another alternative is to list your “trade only” piece there.
As Bill has said, this is the first Comic Art Live and, in a way, a test run and will need feedback to make the next one better and smoother. You can suggest to him adding a “trade only” option next time. However, to reiterate my point, I think the mission here is to offer fresh to market pieces with no guess work as to the price or to offer stale pieces priced to sell—things that buyer-collectors really need in today’s market.
post---script: oh also, I recall Bill writing that anyone who violates the guidelines will have their privileges revoked selling at the next con. Not sure what guidelines though. Something to keep in mind.