LLM's like the AI's you mentioned generally are just really good at predicting the next word. For example, Given an input like "My dog likes" an AI may add the word "treats" to the end. They are so good at predicting the next word that they will write paragraphs that sound entirely human.

So, when they give you strange links, and made up names it's probably because it just thought that stuff sounded good.

You can only trust results if you verify them yourself.

I am not sure if the paid versions are better.

https://en.wikipedia.org/wiki/Hallucination_(artificial_intelligence)

https://machinelearningmastery.com/a-gentle-introduction-to-hallucinations-in-large-language-models/

In short: Language models are not search engines or databases. They make up text. Hallucinations are unavoidable.

You can't trust them. This is still matter of research. Maybe it'll get better in a few years once researchers found good ways to mitigate this.

Perplexity.ai has always provided sources and even has filters you can select by clicking the focus button. I dig it for academics as there's an academic filter plus all sources provided I trust such as PubMed, NIH, SemanticScholar, and NCBI. I also really dig there no account needed, unless you want to implement GPT-4. At times I've had to ask for additional details on the answer provided without GPT, but up to this point its still by far my favorite AI to utilize.