Despite consumer protection, this is still a good motto when buying gemstones. At NEC I was tempted into buying a long rectangular tourmaline from a German dealer just on impulse.
When I inspected it later, it was evident that there were some dark inclusions and usually I quite like them because they add to the character. Not so good was a tiny air space at one corner. I had not got very far with building a setting, before that corner disappeared. An inner voice said “I told you so”. Anyhow I went down to my favourite gemstone place in Cerkenwell and explained the situation. You don’t get to see the actual gem cutter, but I explained to the counter lady that I wished to keep the long rectangular look and could they just remove the minimum from one end to restore the corner.
When I returned to collect it the stone was almost square. Here it is in a ring and I have tried to restore the long look by adding a recess at each end. I suppose a real jeweller would have put in a couple of baguettes. To add some sparkle I made a jagged bezel and burnished it.