Sign of salt water, damage

[Tony Cruiser]

I may purchase a Crownline 240LS 2007 w/ 350 mag with bravo 3. My concern is seller says boat used only in fresh water. Bravo 3 has erosion on drive just before prop, above prop housing (all erosion is on drive). Are there tell tale signs to tell if boat was used in salt water or is the damage to the drive from electrolysis (galvanic corrosion) and would any part of the engine be damaged. Test drive to come soon. Any help would be great.