What is this chargeback issue that everyone is talking about?

[hassan947]

It's been roughly 8 years since I'm working with upwork and I never heard of it but now when I also try to get some attention on fiverr, my friend zone is warning me to leave this platform as amount wouldn't be secure and buyer will scam me with chargeback. 

There must be million of people working on this platform and my question is if fiverr is that unsecure then why all of those people trust fiverr and work here? is this just a rumor or am I really missing something? If it is true then how am I suppose to prevent this scam?