Тhe steps to making a decision are well known:
1. Are the covers better than the average self-published such?
2. Is the editing better than the average self-published such? (free samples should suffice to see that)
3. Do the already published books in the potential author's genre hold good sales ranks on Amazon?
4. Do the already published books in the potential author's genre have a lot of positive and authentic-sounding reviews?
5. Is the contract fair?
6. Are there any complaints online by authors who feel they have been treated unfairly?
Points 1, 2, 3, 4 and 6 will take about half an hour of research to check out, while 5 probably needs actual email communication; the cumulative result should point to a yea or nay answer.
Unless all that matters is having one's book published by a 'real' indie publisher--a valid enough psychological state--in which case only the contract matters, and the possible unfair play.
An additional point--which may or may not matter--is the publisher a one-person operation or not? Sometimes one-person operations suddenly collapse when personal emergency strikes, and everything else stops being important, including you the author and your book. A larger organization can have members struck by individual emergencies yet still function. On the other hand many great agents are one-person operations, so this one is more an issue to be decided by intuition. If the one-person operation has been around, without major scandal, even with some success stories, for a number of years, could be OK. Unless the person in question is by now 90.