Check out your Marketing Optimization section and see what your Keyword Conversions and stuff are. Depending on the cost of the words, you could setup an AdSense account to target the keywords that people type most often before clicking your link. AdSense can cost $$ though if lots of people click but don't buy anything.
Wayne is dead on: 160 unique visitors a day isn't much. If you really want to sell stuff, especially online, you need high traffic.
If you don't mind, you might want to include what site it is here, as certain members might be able to give you tips to increase traffic, or the layout to increase sales.
Look at where your principal sources of traffic are coming from, besides the bookclub website, and then optimize for that. Are you a member on the book club site? If so, post there OFTEN on SK issues and include your URL with some good marketing in your signature line.
With the limited details, it's hard to say for sure, but here are some guidelines:
- Layout: A nice, clean, easy to navigate layout tends to sell more. Take Lube's example, I'd bet the second layout generates a MUCH better conversion ratio. Don't have a lot of flashy crap that visitors get attracted to. You're trying to sell something, so you want to keep them ON YOUR SITE and off someone else's, for as long as possible.
- Optimization: There are TONS of sites on the net, and a relatively small number of people shopping for SK items, so you have to market to them as effictively as possible. Search Engine Optimization is important, and is different for each search engine, so look at the stats and decide which one you want to optimize the best for. In the same vein with layout, make sure your site isn't cluttered with things that would distract your viewer from clicking BUY ME NOW or whatever.
- Traffic: Traffic is huge. You _need_ traffic to sell, because the more traffic you have, the more people see your wares. It's like physical store placement, stores on a well traveled street sell more. You can get traffic by Search Engine Optimization, posting on related forums, finding SK interest sites and asking the webmaster to put a link up (text/image/ whatever) to your site, attending book club meetings. Try to think of different ways to get targeted traffic to your site.
BTW, I don't link how GA shows referrers. I use ExtremeTracking.com to track for referrers and like it much more. YMMV.