I sometimes forget that some of my customers are new to fountain pens as I was once myself. When I remember I include a sheet explaining the use of the eyedropper filler but all the other types of vintage pen can be a little intimidating on first use too. I mostly sell lever fillers and Leverlesses. I need to develop instruction sheets for them too. Boxed pens often come with the original instructions, and that’s the best. I might copy them.
Of course I can’t cover everything and in any case people may have questions ahead of purchase. I’m always happy to advise and inform. If you need help just contact me on email@example.com.