There are good arguments and their are bad arguments. There is good evidence and bad evidence. Ultimately, these things are a part of good science and bad science. And, of course, part of being a good scientist is being able to weigh an argument, analyze evidence, and tell what is acceptable. In short, you need to be able to think critically about (and be justifiably skeptical of) the information and ideas that you are presented with. Developing these skills takes time. And there are no black and white lines that clearly separate the good from the bad. That said, this graph gives you a good place to start.
So give this graph a look, and see how many other kinds of "bad science" you can think of.