Ask them. They may not tell the truth, but when people put a status up it also could be a lie.
Its complicated is often used by people that are married but don't want to admit it. But it is also used by people who have recently broken up and are not sure where they are going. And by people who have lost an SO to death and are not ready to get involved. And any of who knows how many other reasons.
As true for anything on the internet, you can never know for sure.
You can't not really, unless you trust that person, and as for whether it say's on my profile and for others I have mine as no comment because it's really no ones business and some people put it there to let people know that they are with someone and don't want to be bothered in that way though because lets be honest the internet and this site is filed with a lot of creeps and perverts and to be fair this really isn't a dating site so yeah.
You can't tell and never will be able to unless you meet them in real life. People lie over the internet all the time and with the magic of photoshop they can "prove" their relationship status to be anything they want.
well to be honest, I'm not really sure why you have to be. i mean if they don't wanna put the right thing on their profile, okay. if u really wanna know, just ask, or you'll most likely see them talk about it on the threads.
for me i don't find it a big deal to have on my profile so it isn't there at all.