negotiating the price when buying an apartment

Always heard there is very little room for negotiation, we got 5k off but couldnt get them to budge on any more

seems to be more room for negotiation in lettings rather than Sales market.
Very much depends on the seller and if a developer or private seller. Always worth a try

If you're not in a rush, and you have other properties that you fancy, try 15%. Remember, everything is negotiable, it really depends on the situation of the seller.
If time is on your side, you have the upper hand, imo.

Thanks so far guys, I'm in negotiations right now and will tell about my experience once the promise of sale is signed.

We had one experience where the agent decided to negotiate down off her own head. The result was that the vendor upped his price and the deal fell through. As it was, we ended up with somewhere even better, even if we did have to move up €20K up the price range, but still got a bargain. Be realistic, not greedy; set your target. Look at the circumstances of the sale, as this can be a big factor in how keen the vendor is to sell quickly, but remember that fairness cuts both ways.

From my experience now, I can say that generally getting 5-10 % off the asking price is totally realistic. Of course it depends on the individual seller and your negotiation position and your negotiation skills.
For the apartment I got now I started with 15% under the asking price and the deal now was 10%.
Without having other options and being chilled about the sellers reactions, I definitely would have ended significantly higher. It's easy for the agent to lure you into making higher offers. He will tell you that there are other people interested in buying etc.. And even if you know it's probably just estate agents tactics, it will influence your offer making, so try to stay as rational as possible and play it cool even if you don't have other options...