Fluoroscopy is a moving-picture X-ray. Developed in the late 1800s, it has valid medical applications to this day. Using it to fit shoes began in the 1920s, when the risks of ionizing radiation were not well understood.

You and a salesperson peer into viewing ports to watch your bones moving in the shoe as you wiggled your toes! Very occasional use was probably not too awful, but radiation damage is cumulative, so frequent use was another story. Salespeople had cumulative exposure risk from proximity to poorly shielded devices. One salesperson rad injury required an amputation. They were fascinating to use, and children would do it just for fun.

US scientific orgs such as ACXRP issued warnings as early as 1931. Pennsylvania banned them in '57, and Switzerland in '59. By '70 they were mostly gone from the US, Canada, and Europe. A few hung around into the early '80s, illegally or inadvertently.

A 1938 unit at the US National Museum of Health and Medicine.

Most of the alleged photos I found of people using one failed an AI checker. The photo below passed, but... it's getting harder to know for sure. I'm tryin' here!