If you have clients who can call you and say probably that "blue" and you know, but not telling this is "blue" part no, I want to know what are you doing (selling), happy to take over and look after these "customers"*
Since you ask...
I work at a model railroad museum/exhibition and we have a small shop that specializes in model railroad stuff, including the rolling stock. Example from the other day: A returning customer calls, asks if his previous order has come in. The answer is "Not yet", so he asks if we have two K wagons in stock and if not to order them for him.
If you're not a railroad fan, you may not know what a K wagon is, and that is perfectly fine. It's a simple two axle flatbed wagon that used to be extremely common in 1950's and 1960s. But that is it. That is all the narrowing down that the term K wagon implies. In real world there are (were) countless subtypes of that configuration that were used by probably every railroad company in the world, each a bit different than the other. In model railroading world, things are even more complicated since on top of real world companies, there are model making companies, multiplying the number of choices. On top of that, in real rail world there is something called revision, which is a mandatory periodic check of the rolling stock, accompanied by new markings and potentially physical changes. Manufacturers of model railroad rolling stock take this into consideration and often produce the same wagon, but from multiple different revisions, of course as separate catalog numbers.
For this particular customer, I know that he collects models made by a certain manufacturer, I can even make an educated guess as to what real world railroad company markings he would like on his model, and know that he doesn't particularly care about revisions (some modelers are quite anal about that stuff), so I could pick something for him specifically.
With all that being said, I can't possibly know the catalog number for that wagon. We are a distributor for about 20 manufacturers, each having thousands of products. If we don't have that on a shelf (or even if I don't find it with a cursory glance), I have to take a look at the computer to see if we have it, and if not order it. For either of those I need the catalog number, and to find that out I would need to actually go through the physical or digital catalog to find it. That takes time.
But that is not nearly the worst type of the calls we get. It's not uncommon for people to ask: "Do you sell trains?", "Yes, we do." "Do you also sell wagons?", "Yes, we do." "How much do they cost?", "Anywhere from $10 to $250 for wagons, much more for special edition locomotives." "Oh, can I come and have a look?" "Yes, we are a shop."