As with anything else, use your intuition, read between the lines, follow the incentives/money.

Based on the rating they give it does seem like a questionable source.

But if you want to go down that rabbit hole of who is or who isn't a questionable source based on some fact-checker you will eventually reach the question, how do we know that our fact-checker isn't biased? who funds the fact-checker, are there any political motivations over-ruling journalistic integrity, etc. And then eventually you arrive at a fact-checker that fact-checks other fact-checkers. And you can keep going down that rabbit hole forever or you can learn to use your intuition.

I will also say this: Even a broken clock is right twice per day.

And in the same vein, Even a questionable source can write an article based on facts every now and then.