Most often it is direct, like: Do you have any red glass? (No, red looks brown with a mat finish, but I listened and made red in other ways). Other times, it is simply a matter of reading between the lines, like: Could I special order one with a larger top section?
Making a couple of special orders like that, I saw that it was a good idea. So last week when I ordered plate glass, I got them to cut each piece one inch wider, one inch higher. Presto, the new 'improved' kaleidoscope wind chime. It's surprising how much just two inches changes the look.
Anyway, thanks again to my customers for all their good ideas.