A first step you can take to verify the quality of the publisher or journal is to see if the publisher is a member of quality controlling organization or if the journal is indexed in a quality-controlled database. If the publisher or journal is not included in the sources below, it doesn't automatically mean that the publisher or journal is predatory or questionable. What you can do then is to look closer at them from the viewpoint of the control questions presented below.  

Quality controlling databases and organizations
 

Journal databases

These two databases have a quality procedure for the journals they index. They are also looking at other aspects which don't deal with the quality aspect but rather with their impact on the research community in the form of citations. This means that there are many journals of quality that are not indexed in the databases. However, if you find the journal in any of these databases you don't necessarily need to go further with the quality control.

• Scopus 
  Scopus has a policy and methodology that they apply to the journals that are indexed in the database (Journal selection criteria) as well as continuous control (Title Re-evaluation). The evaluation policy and control concerns such aspects as editorial policy, peer review, frequency etc.

  Content Policy and Selection
   

• Web of Science
  Web of Science has a policy and methodology that they apply in the journals that are indexed in the database (Journal Selection Process). The evaluation policy and control concerns such aspects as editorial policy, peer review, frequency etc.  

  Journal Selection Process
   

• Directory of Open Access Journals - DOAJ
  DOAJ indexes open access journals which meet their best practice which, among other things, includes aspects such as peer review, editorial board, contact information, ethical publishing principles, retraction policy etc.
  
  Principles of Transparency and Best Practice in Scholarly Publishing
  DOAJ: Journals added and removed
   

• Journals Online
  INASP (International Network for the Availability of Scientific Publications) is an "international development charity working with a global network of partners in Africa, Latin America and Asia", for them to gain access to and be able to use information resources to solve the developmental issues at hand. One of the projects of the organization is the development of quality based journal databases. Journals Online contain, as of now, six databases: African Journals Online (AJOL), Bangladesh Journals Online (BanglaJOL), Central America Journals Online (CAMJOL), Mongolia Journals Online (MongoliaJOL), Nepal Journals Online (NEPJOL), Sri Lanka Journals Online (SLJOL). Journals Online have quality criteria although they do not have any follow-up control of its enforcement.
  
  About the JOLs
   

Organizations

• Committee on Publication Ethics (COPE)
  COPE was created by a couple of British journal editors in 1997 but now has around 12,000 members all around the world. COPE offers support to publishers and editors regarding publishing ethics. Under the tab Members, you can search for both publishers and journals.
  
  Core Practices

• International Association of Scientific, Technical, & Medical Publishers (STM)
  STM is a leading organization for academic publishers, among others, with 120 members in 21 countries. They have produced ethical guidelines for their members.
  
  Code of Conduct
  
  Members List

• Open Access Scholarly Publishers Association (OASPA)
  OASPA represents several open-access publishers, both journal and book publishers, which through their membership have gone through a vetting process based on many quality criteria.
  
  Membership Criteria   
  
  Members

Blacklists

• Beall's List of Predatory Journals and Publishers
  Jeffrey Beall is a librarian from the USA who had a list of predatory publishers and journals under the name Scholarly Open Access but which was taken down at the beginning of 2017. The list is still available under new management and includes continuous additions as well.

Questions you should ask yourself when you check the quality of a journal

If you haven't found the journal or publisher through the sources above it doesn't mean that they are not legitimate. It might be a new journal and the editor hasn't yet applied for membership or indexing in DOAJ. Presented below is a number of questions you may pose when checking the journal, primarily through its website.
 

• Has the publisher or journal any of the characteristics mentioned in the earlier section (Questionable publishers and journals: Characteristics)?
• Do any of your colleagues know about the journal?
• Have you read any articles from the journal before?
• Do you recognize anyone in the editorial board?
• Do the members of the board mention their board membership on their profile pages?
• Do you recognize any of the article authors?
• Is it easy to identify and contact the publisher or editor?
• Is it stated which type of peer review they use?
• Are the articles indexed in any of the databases you use yourself and which your potential readers might use as well?
• Is it clear if there are any author fees included (APC - Article Processing Charges) and when they should be paid?

Think. Check. Submit.

Think. Check. Submit presents a checklist as the one above with questions you should ask yourself before submitting your manuscript. The resource has been developed by, among others, COPE, DOAJ, OASPA, INASP etc.