Well it greatly varies from author to author, as some will have larger portfolios than others, and different people are selling different types of music. It’s a fact that corporate / motivational music sells more than say experimental and abstract music. Some authors choose the business model of building up a large portfolio and regularly upload several times every week (this is a proven method to establish yourself on a stock music site), whilst others focus on having smaller and more specific portfolios.
My sales to items ratio is about 9, but I’ve deleted some older tracks so it would be more like 8. Again, this differs greatly depending on the genre, type etc. I wouldn’t say it’s a bad thing to have less sales than items uploaded - have a look at the top selling monthly SFX authors - Sound-Ideas and FX-Pro Sound, who both have very low sales-to-items ratios.