One thing I found in my on-line investigation. There were complaints about every e-pub. Granted, some were mild and restricted to one person's experience, some were more serious in nature.
I am active with about 3 right now. I did have more. One of the ones I dropped, Silver Publishing, has never fully paid me for all royalties. I requested and received the rights back in Nov 2012 and have moved on.
The three I am currently with are not perfect either (who is, neither am I!)
Here are a few things I looked for and found in my internet surfing:
Personality complaints should be taken seriously, but not everyone may have had the same experience. If more than one author complains, it should give you pause. Know that for every one author that speaks out, there is usually five more silently fuming on the sidelines.
Most important thing: do they pay on time?
This is a red flag issue. Stuff can happen, a payment may be late for whatever reason, but if it happens to more than one person on a consistent basis, avoid like the plaque.
Lesson I learned: Go through one complete royalty cycle before submitting something else to a publisher. This will give you insight to their editing process, promo, and payments .
Join groups and interact with other authors within that pub. Do the authors turn on each other like a pack of hyenas? (And I have seen this more than once with epubs) That also should give you pause. It shows a layer of dissatisfaction, or on the other side of the coin, a few of the authors could just exhibiting temporary diva behavior. Make the judgement call for yourself. Observe how the publisher responds to supposed diva behavior, that will tell you plenty as well.
Editing seems to be another sore spot. This is entirely subjective and varies from pub to pub and editor to editor, so look for a general, consistent opinion on a pub's editing procedures. Check out reviews on the pubs books. Is editing issues mentioned more than once? There could be a potential problem. I have had good and bad edits, so expect the same wherever you pub.
Check twitter and other social media, is a pub doing promo on their authors, and I mean all, not just a select few? That is a good sign. It is tempting for a publisher to constantly promo their top sellers, but I respect a pub that spreads it around, especially to newbies. Shows professionalism and fairness.
Read the submission guidelines carefully. Be prepared in some cases for a long wait for an answer, or after you are offered a contract, a long wait until publication. Make sure your story is a good fit for the epub in question.
Hey, I am not perfect, nor do I have all the answers. Submitting to any publisher is a judgement call. Stay informed, make decisions for yourself, not based solely on one person's experience. If you find an epub that pays on time, treats you with respect, and isn't always a pain in the balls, then they are a keeper! :)