I can tell you from experience, don't expect to sell out of product each gig, but one thing that will help sell is to mention the product specifically from the platform. If you can highlight one or two songs from the CD, maybe some songs you don't do in your set, or maybe talk about one of the better songs from the CD that is in your set.
You can always find out how the audience reponds on a certain song, then if they repond positivelym on the song, mention that it is on your CD for sale and maybe give some background that could relate to your audience. I've seen us sell one or two of a product, then go to the next conference and mention the same product, talk it up from the platform, then sell out of that product before the end of the conference. It's just marketing strategy.
hope this helps.
Jeff