Many times it can be hard to judge the size of a specimen by looking at the pictures. So it is important to pay attention to the measurements. I know how frustrating it is to purchase a specimen that is smaller than I thought when I saw the pictures. Some place I sell it is not legal to have my hands or anything else on the pictures. The reason why is that some sellers (for example on ebay) make the photo in a way that the stone looks big compared to their hands. Also remember that a 2 cm crystal is in fact 8 times bigger than a 1 cm crystal (it is twice as high, twice as long and twice as wide). I believe many do not think about this when they buy. At the picture below I have added one 1 cm crystal, one 2 cm crystal, one 3 cm crystal and one 4 cm crystal. As you can see there is enormous difference.
At the same time, when it comes to zircons you will often see damages on the crystals. If you are looking for big/huge crystals there will almost always be some smaller/bigger damages, and it is extremely rare to find huge crystals wish little damages. So this is also reflected in the prices where zircons with little damages can be many times as expensive as zircons with some damages.
Even for small zircons you will almost always find some minor scars, but sometimes of better quality. When buying from me, know that all measurements are given in height x length x width. I do not mix, so it will always be in this order: 1) Height 2) Length 3) Width. It can sometimes be hard to do exact measurements, as stones are not square, but I try to be as precise as possible, so what you see (and read) is what you get.