To-date, I have several collections out for sale, each with a different focus.
The Next Stop - 3 stories will Twilight Zone-esque twists
Elusive Enchantments - 3 unusual romances
The Space Hotel Series Collection - All 5 of my Space Hotel stories
Lunchable Short Stories - 5 fun, slightly humorous stories to be enjoyed at lunch
Of the four collections, the Space Hotel one is definitely my best seller. I credit this largely to the fact that I had Celebrity Space (part 1) up for free for several months. Before the free period, it didn't sell at all.
The rest of them I get the random sale here an there but nothing consistent. I have standalone short stories that have been out on the market long enough that they are starting to pick up slow, steady sales. This just hasn't seemed to happen with any of my collections.
I suppose I could go through and pick apart the "presentation" of each collection. You know, analyze the cover and the blurb... things like that. But I honestly think that all of my stories and collections have a pretty uniform appearance. I mean, is the cover of A Model Railway Man really that much more thought provoking than The Next Stop?
The purpose of this post was not to gripe and whine about people not buying my collections. Merely to address what I think are two important marketing points. The first is that it is important to have both standalones and collections on the market. Don't miss out on that sales opportunity if you primarily write short stories.
The second thing goes more into the realm of speculation. Why do the the standalones sell better? Maybe people really are reading a lot on their cell phones or on their Kindle in the doctor's office. Despite the naysayers, maybe there really are cult followers for short stories still.
I really wish there was some way to conduct a study on this...