If you just want to know, without further investigation, that’s going to be very hard. People say a lot of things, and often aren’t clear themselves if it’s something they actually know, or just something they’ve heard. All that’s happened is that something interesting / helpful has popped into their mind and they’ve shared it.

If you are willing to discuss it, but don’t want to be rude by asking “do you actually know anthing about this?” you can just ask follow up questions, asking for more info / details. That way people who really know can answer, and people who don’t will probably just not answer or say that they just read it somewhere (often they’re not trying to deceive, just sharing something interesting they heard about).

But as others have said, just be sceptical of stuff you read, especially on the Internet. Lots of people have first had experience of something and still have unhelpful or strange takes on things. People massively over estimate how representative their experiences are, and if you get two experts in a room they’ll pretty soon be disagreeing about something they both know throughly.