Bitcoins once sent can't be taken back. So check more than double times before any transaction. Also, so many scammers here to cheat you. Now a day most important thing you hide your identity, before purchasing any bitcoin. so the question is how to hide your identity and how to conversation with the unknown person. Now a day so many ways to work online without show your original number. One of the best ways to work with an unknown number is WhatsApp. you can use your WhatsApp without any phone number or sim card. If you think how to use WhatsApp without phone number then here is a simple article you can read step by step instruction. It works in all platform windows, android & ios.
how to use WhatsApp without phone numberSo before dealing you can use this method to an unknown person and save your identity.
typically you should use authenticator apps like google authenticator or authy for more security. Most modern exchanges have this.