A few points worth clarifying:

As another user pointed out, pseudoscientific journals and predatory journals aren’t the same. As you pointed out, pseudoscientific journals are generally easy to identify because they have a very clearly stated agenda typically. This means they will publish anything that places their ideas in a favorable light and are generally not objective. They tend to push garbage “science”.

Predatory journals are journals and publishing firms that have what is effectively a pay-to-play scheme, where authors are enticed with minimal peer review at relatively high publishing cost. Meaning, any crappy study can/will be published so long as the authors pay the publication cost. There’s a list online (Beall’s List) of what might be considered predatory.

Now, I will also point out that the authors paying is not what makes this unethical and damaging to science. The vast majority (if not all) scientific publishing is contingent on the authors paying the publication cost and these costs are going to be especially high in open access journals (e.g. PLoS, which is not predatory). These costs are only incurred when the journal agrees to publish after getting positive recommendations from reviewers. Predatory journals forgo the review, and simply publish.

Fraudulent work (i.e., faked data) is likely to be present in any reputable journal, albeit at low frequencies. I say “low” because science is increasingly moving toward an open data model of publication where the raw data sets associated with study must be available publicly, including code used to produce results. While there aren’t loads of people reanalyzing published datasets, the possibility that someone might could be enough to deter most people from making shit up.

I wouldn’t let the Wakefield example spoil the wealth of good studies that’s been published at the Lancet. At this point the only people giving that study any credence are Brain-worms and his ilk. A better bet is to look for retractions issued by the journals. This typically happens in the event of fraud, non reproducibility, fundamental flaws in the study, etc.

Source: I’m an academic scientist and actively publishing.

Tldr: look at Beall’s list for predatory journals; don’t worry too much about fraud in reputable journals; look for retractions if you’re really worried.

Course IDs vary from university to university—when I was an undergrad, lower div classes were <100, upper div between 100 and 199, and grad level classes 200+.