I too have corresponded with Beall and questioned him about various decisions. He always answered courteously and often convincingly. 

Contrary to what some of his enemies said he did make clear his criteria: http://publica.upc.edu/sites/default/files/arxius_site/criteris_editorials_fraudulentes.pdf.

I know that many librarians used both DOAJ and Beall as aids to advising their patrons and why not both?

I stopped interacting with Beall when he made it clear that Open Access was seen by him as an invention of “communist” Europeans and anti-American and he denied any real arguments for this publishing model: http://triplec.at.dd29412.kasserver.com/index.php/tripleC/article/view/525.

The open access movement is a broad church and there are of course those involved who are “anti-corporatist” but there are plenty who are not and there are many who accept the arguments for open access but did not think it would work as a publishing model. This was my position.

Anthony