The man suffered "potentially serious injuries" after being attacked at The Range shop in Willenhall on Sunday.
Emergency services were called to reports of a fight at the homeware store on the Longacres Industrial Estate shortly before 2pm.
The injured man was taken to hospital after initially being treated by staff from The Range.
The shop was shut soon afterwards but was back open as normal on Monday morning.
A 34-year-old man from West Bromwich has since been charged over the attack.
A West Midlands Police spokesman said: "A man in his 30s suffered a head injury and has been taken to hospital. The extent of his injuries are unclear at this stage.
"A hammer has been recovered for forensic examination and CCTV enquiries are ongoing."
In an updated statement on Monday afternoon, the force added: "Daniel Lawley, of Allerton Lane in West Bromwich, has been charged with possession of an offensive weapon in a public place and grievous bodily harm with intent after a man was injured in The Range store in Longacres, Willenhall yesterday.
"The unemployed 34-year-old is due to appear at Dudley Magistrates Court today."
A spokesman for The Range said: "We would like to commend the store staff at The Range Willenhall for their courageous actions regarding the incident that occurred on Sunday.
"Shop floor staff took appropriate action by administering first aid to the victim whilst the management team swiftly evacuated the building and phoned emergency services.
"This was all completed in an impressively calm and efficient manner with customer safety coming first in every instance. We are pleased to announce that the store has reopened today.
"We would like to thank store staff and the emergency services for their help and wish the victim a fast recovery.”
A West Midlands Ambulance Service spokesman confirmed that crews treated one man for "potentially serious injuries" before taking him to hospital.
Anyone with information is urged to call West Midlands Police on 101, quoting log number 1972 of October 11.