What exactly to you mean by reliable? Is it guaranteed they will ship your bag once you purchased it? In that sense yes, BlueFly is reliable. I've never had them cancel an order on me. Or are you asking about authenticity? In that case, again, Yes, BlueFly is reliable. Many PFers including myself have purchased Fendi bags from them and they all have proven to be authentic.
I've purchased fendi, chloe, and balenciaga from BF and all were authentic. I think the problems they had years ago were from people returning fakes (the old bait and switch) but they protect themselves now because the bags come with a tag that must be attached for returns.
Their return policy is great too, so you could always return something you weren't happy with.