A passing bicyclist called police after seeing a masked man spreading the acid graffiti on a shop wall Sunday night, ThinkSpain reported Tuesday.
At least 20 of the 57 shops suffered extensive damage to their windows and permanent stains.
One of the shop owners, whose name was not reported, said insurance will not cover the damage since the windows are not broken.
"We've had the same policy for more than 60 years and they've never once met a claim for this type of vandalism," the retailer said. "So far, we've paid out over 6,000 euros [$7,971] in repairs through mindless attacks on our premises."
The vandals even damaged the Oxfam shop on Marques de Dos Aquas, ThinkSpain reported.
"We've been here 20 years and the public have always respected us, but not now," the manager said. "All of us who work here are volunteers and Oxfam is a charity, so it will cost us dearly to repair the damage -- out of money that should be helping to save lives in the third world."