I've looked at it for items on occasion. What I have noticed is that I need to specifically go to the sight to find something. Google search doesn't seem to pick things up if they're listed there. It's the same for Trocadero. The only one that sows up SOMETIMES is Ruby Lane. I guess the bottom line is someone has to know about these sites in the first place and go there directly to find your item. Wide Google and Bing searches don't seem to work.
Ruby Lane, 1stDibs and etsy do pop up on broken-link infested pinterest, but never Trocadero or tias. Almost forgot they were even there.
I'm in the UK and haven't heard of those sites before. Having had a look I think I'd be unlikely to buy from them unless I was very specifically looking for something.