Is a journal that is on Beall's list but is also in Scopus a predatory journal? I have seen a journal, in the Computer Science field, that is predatory according to the Beall list (sorry if its not well written), but I see that this journal appears indexed in Scopus and Scimago; so I was wondering how to determine if a journal is predatory or not? 

For example, I know that even some journals from Elsevier or Springer charge different prices for publishing an accepted article, and according to some colleagues if a journal charges for publication then it could be a predatory one, but the aforementioned editorials charge also so to whom believe?

I was also wondering if the B list is also accurate, I am starting to have my doubts about it.
Indexing in Scopus does not necessarily mean that a journal is not predatory. From the guidelines for being indexed in Scopus:


  -The Journal should consist of peer‐reviewed content
  
  -The Journal should be published on a regular basis (have an ISSN number that has been
  registered with the International ISSN Centre)
  
  -Content should be relevant and readable for an international audience (at minimum
  have references in Roman script and English language abstracts and article titles)
  
  -The Journal should have a publication ethics and publication malpractice statement


These guidelines could potentially be satisfied by a journal that Beall's list considers predatory. Many pay-to-publish journals advertise "peer review", but it may not even be solicited/may not matter in the "decision" to accept the manuscript. 

There also can be information on why the specific journal or publisher is considered predatory on https://scholarlyoa.com. I generally have high confidence in Beall's list--predatory journals do not have a great incentive to turn legitimate.