Here is an adage I always remember;
Lures are like fashion accessories, some are just fads and are great for a short period of time, some are classics that will always be used and will always catch fish.
What I do as a buyer of vast quantities of lures is look for a lure that does something different. I can, and have, bought hundreds of, say poppers, in the past. Now why do I prefer a certain popper over another? Usage, being an angler really helps. I loved the Rapala Skitter Pop, but although it is a classic I did find it tried to walk a bit and would tangle, therefore I went off it. I find the Feed Popper does what I want from a popper so I chose that. There was alure I used to absolutely love called a Cultiva Tango Dancer (Owner), now these lures caught us a shed load of fish, but once again they also were known as Tangle Dancers amoungst us. Then along came the Z-Claw, very very simular but doesnt tangle, so thats my choice now.
Diving lures; I need a few sizes and shapes and a few colours, a few silent and a few rattlers, these few of each in these add up to a few thousand lures, its like combinations of numbers. Man think about the numbers here, say lures of 80mm, 90mm, 110mm, 115mm, 120mm, 125mm, 140mm, 145mm, 150mm, 175mm and 200mm, in say 3 or 4 shapes, in say 4 colours, and silent or rattling, this is hundreds already, and then buy say 20 of each for stock, maybe 50 or 100 of the good colours. Then you will still get customers wanting co,ours and lures you dont have.....ahhhhhhh, retail, I love it.