I'll post the same advice my dad gave me:
1) Never buy from an airport shop, they know you're never coming back (so I guess by extension, an internet shop)
2) DIF diamonds people buy as investments, and they're not worth forking the premium for stones less than a karat. Drop down 2 scales on all fronts and nobody will be able to tell the difference without taking out a DIF stone and putting it next to it. Even then most would need a loupe.
3) The raw material cost of diamond to ring ratio, try about 1:0.1-0.25, not much more.
4) If bringing a stone in that has not been serial numbered/certified that you can check to be set by a jeweller, never let it out of your sight while they set it (Shouldn't take more than 30 mins to set). Follow it into the workroom, etc. if it is serialed, make sure you know and can determine that it is the same stone that you have given them.
Hope this helps
1) Never buy from an airport shop, they know you're never coming back (so I guess by extension, an internet shop)
2) DIF diamonds people buy as investments, and they're not worth forking the premium for stones less than a karat. Drop down 2 scales on all fronts and nobody will be able to tell the difference without taking out a DIF stone and putting it next to it. Even then most would need a loupe.
3) The raw material cost of diamond to ring ratio, try about 1:0.1-0.25, not much more.
4) If bringing a stone in that has not been serial numbered/certified that you can check to be set by a jeweller, never let it out of your sight while they set it (Shouldn't take more than 30 mins to set). Follow it into the workroom, etc. if it is serialed, make sure you know and can determine that it is the same stone that you have given them.
Hope this helps

) to Brussels, a short train journey to Antwerp and the diamond quarter and take your pick.