Real Est. zoning question.

So the shop in question is zoned for repairing broken windshields and such. Owner tried to sell it over the years but was told that zoning could go only to residential. His shop is grandfathered in and cannot be used for any other commercial purpose except auto related.

A guy wants to buy it and put in a plumbing business... just parking his trucks and store parts and fixtures inside. He was told by seller's lawyer that this could work if he doesn't change the signage on the front of the building.

Does this make sense?