Robert Hoge has this suggestion for small literary presses which promote their books at conventions:
Don't try to guilt $25 out of me as a purchase-as-charity sale to support a small press. Yes the publisher has put lots of effort into the book and will almost certainly make a loss on the publication. But don't say you're going to bar the doors until everyone buys a book because the small press publisher deserves our support. Small publishers deserve and get our support because they publish shit-hot stories. If you don't at least try to sell me on buying the book because of its quality then you're not doing you're job and you don't deserve a sale.
I have been to too many launches where the only call to action is "buy the book so you can support the publisher's hard work and they can do more publications." Harper Collins won't be telling me to buy the books at their launch because Rupert Murdoch needs the money. They'll be telling me to buy the book/s because if I don't I'll be missing the hottest YA fantasy of the year or the best science fiction debut since Mary Doria Russell.
Since Hoge is a judge for this year's World Fantasy Award, I'd suggest small presses take his suggestion under serious consideration.