I happen to know a few folks who work in this field (detecting fraudulent scientific papers). This is a bit of an insider knowledge, but there are science sleuths who are fearing for their lives... there might be some seriously shady stuff going on behind research paper mills, but I don't know who will be the one digging those up.
If it is just on an individual level though methinks Retraction Watch does a decently good job at informing what might or might not be trustworthy