Haggling in Diamond Shops

[itwontbeeasy]

I've gathered (both from the shops themselves (Hatton Garden, London) and also from places online that it is quite normal to be able to haggle over the prices for diamonds.
Has anyone done this and what % is reasonable to try to aim for?
Does anyone know what the mark up is for Diamonds somewhere like Hatton Garden?
(My uneducated guesstimate would be 40%+ ?)

Thanks for any help!

 

[Garry H (Cut Nut)]

1. knowing the mark up does not mean the vendor will haggle more or less.
2. when you get near the botttom, pull out your credit card and if they say "hey that is a cash or cheque price" you know you are as low as you can go.
3. My clients can get me down 5-10% and my staff are tougher than me. But if someone produces a pricescope report I will panic aa bit more!