I don't think there is currently a way to know that a cash sale exists relating to a specific case UNLESS you open each cash sale to see if there is a case reference on the basic info page.
Even though it does link back to the case from within the cash sale, there is no similar link/reference on the case side linking back to that cash sale. Many times there are items pertaining to cases purchased on a cash sale and it would be helpful if there was a link to it in the goods & services page.
Have run into this very issue...it would be extremely convenient if on the Goods & Services page that the cash sale would show as a tab, much like the pre-need contract appears. There are numerous benefits to having it appear in this location versus somewhere on the case summary page. Am excited to see this idea put into action and am hoping sooner than later.