The washer that stops water flow is probably bad, since it is quite old. Repair or replace is your choice. On a commercial building, most at soldered to prevent theft of the whole faucet. You could disassemble it after turning off the water supply to it. Check the condition of the washer and go from there. Most commercial faucets are required to have a back-flow preventer either built-in or installed. This adds to the cost of replacement.
if you have never made a mistake, you probably haven't done much.