It is difficult for the staff at the museum. They have to staff the shop, sell tickets for the museum, answer phone calls for the museum and for the National Park (which owns and runs the museum) and field general enquiries because the museum also acts as the local Tourist Information Office. There are never more than two staff on duty at any one time and sometimes (e.g. lunchtime) there is only one. There was only one hard-pressed lady on duty when the incident happened with my pen, so I can hardly blame her.
I also have to bear in mind that the Museum/National Park don't charge any commission for selling my pens, the proceeds from which go towards repairing and rebinding rare old books of local interest in a collection which is held in trust for the people of Wensleydale and is housed in, but not owned by, the museum.