There are a lot of great small publishers! There are also plenty that writers should steer clear of. In my Ask the Agent Question of the Day, I talk about red flags to look out for when evaluating publishers.
https://www.tumblr.com/literaticat/774664679770537984/i-saw-you-comment-on-a-blog-called-my-cautionary?source=share
https://www.tumblr.com/literaticat/774664679770537984/i-saw-you-comment-on-a-blog-called-my-cautionary?source=share
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Also, here's a great resource people can use to evaluate a "hybrid publisher": https://www.ibpa-online.org/page/hybridpublisher