From time to time, there are people who will use the anonymity of the internet to pretend they are someone else. I've witnessed this happen a few times through the years of playing FFXI and FFXIV. It's always creepy and I don't really understand the purpose of it. For this reason I "always assume dude" unless I hear the person's voice. There is voice augmentation software out there, too, so you can't even always trust that. Red flags are usually things like not wanting to get on voice chat, or getting on voice chat "only to listen" and being a loot-hog.