In a salt water environment, rebar corrosion is accelerated. And significant corrosion causes the steel to gain in volume, resulting in tensile forces in the concrete in front of it. Enough tension, and the concrete delaminates and breaks (spalls) off. If you have the opportunity, go back and lightly tap on all of the columns on the property, wherever you can reach, with a hammer. Locations where you hear a hollow, dull thud sound (as opposed to a higher-pitched, "ringing") indicate delamination, corroded rebar underneath, and eventual spalling.
As a DOT bridge engineer in a former life, I've supervised and inspected the repair of hundreds of similar (bridge) columns. Properly done, such repairs can last dozens of years; improper repairs will not last a year in salt water environments. In severe cases, temporary shoring has to be installed to support the overhead loads while the deteriorated concrete in the columns is chipped away, removed and replaced.
Before making an offer on the property, I'd strongly suggest you get a few lump sum quotes from qualified contractors for completely repairing all of the columns. You may find the quotes to be larger than the asking price.