1. Publisher integrity - A few starting places to consider
Check if they are a COPE member : "COPE is committed to educate and support editors, publishers and those involved in publication ethics with the aim of moving the culture of publishing towards one where ethical practices becomes the norm, part of the publishing culture. Our approach is firmly in the direction of influencing through education, resources and support of our members alongside the fostering of professional debate in the wider community."
Or if they are a OASPA member (Open Access Scholarly Publishers Association) : List organisations and individual publications that are recognised as Members of OASPA. Approved members have been through a rigorous application review process and adhere to OASPA's Code of Conduct.
Think. Check. Submit. - helps researchers identify trusted journals for their research. Through a range of tools and practical resources, this international, cross-sector initiative aims to educate researchers, promote integrity, and build trust in credible research and publications