While using reliable/decentralized exchanges fits as an answer perfectly, sometimes it may be a trusted exchange selling virtual Bitcoins. That's right, virtual virtual currency.

For example, I would avoid purchasing BTC on platforms that only give you Bitcoin on paper like purchasing Gold stocks. You don't actually end up owning Bitcoin on there - it's just you paying the price for something they don't truly sell, if that makes sense.

Back when the immigrant crisis was a thing in Europe, banks selling gold have been hoarded by people trying to physically withdraw their owned gold - and that is a very big issue. I'd rather own it physically than virtually, the same way I'd rather own Bitcoin in my own wallet rather than a number on a random "reliable" website.

Who, exchanges? Oh, there are lots of exchanges doing what is known as wash trading, faking their volumes.

How do you know who bought what? Well, you just don't. But you don't know if Gold's market activity is 100% legit either - and I can assure you it isn't.