In my experience, as far as genuine items go, yes. My recommendation to you is, research the store you're buying from, because your experience can be 0 or 5 stars depending who you're buying from.

I bought a new Valentino bag and received an used one from a store called Gente Roma. Farfetch did nothing other than contact the store and politely reply back to me that there was nothing they could do about it! They made the sale, they're making money off me, off course they should have done something. Nope. I could return the bag, which was an option regardless. Gente Roma was so disonest about the condition of the bag, I was afraid they would blame me for sending back a used bag and only give me a patial refund. I felt my safest option was to keep the bag.

On the other hand, when I bought a pair of Valentino shoes from Exelsior Milano my experience was flawless. From the fast shipping, to the packaging to shoes that had never been opened.

Moral to the story: if Farfetch doesn't have to get involved, you're golden. If not, don't bother with them. Call the Pope or your credit card and dispute your charges instead. You'll have a better chance of getting something.

Ordered 5 items from them and never had any problems

I have purchased at least 25 items from Farfetch without any problems. I usually always buy during their sales events. November to January and early June/July. I get what I want when it starts, usually 50% off. Later I buy stuff when they reduce to 60% off with free shipping. I am in Canada and a male. Shipping is usually 2-5 business days. Adam

I have never had a problem with authenticity or payment and they're shipping is fast (Australia in about 4 days). Just make sure you've done your homework on prices. Sometimes there will be more than one boutique with the item you want - prices for the same item can vary heaps! For example, I bought a MK's silk shirt that was on sale but full price and not on sale at another boutique.

It is safe site. No worry at all, where do you live? I'm in Australia, I had few times experience to shop at farfetch, never got problem, just sometimes they took bit long to process my order, but their customer service is good, you can email them anyway.
Good luck

Yes it is a 100% safe
I have been shopping with them for six years now.