Normally an outboard is run in fresh water for enough time to bring it up to its operating temperature. The lower end is drained of gear oil and refilled, and most good mechanics will lubricate the other moving parts. Fuel tanks are filled and a fuel stabilizer added. With a small outboard dangling on an outboard bracket, this isn't an easy job. When we see an engine that looks beaten-up, it generally has been.
Some people paint the submerged areas of outboards with anti-fouling bottom paint.
Most bottom paints are not made for protecting aluminum. The reaction causes deep corrosion in the aluminum that can seriously deteriorate an otherwise good motor. There are special paints formulated for this application. A well-maintained sailboat outboard of up to 10 hp is seldom affected by age. My 1960 3hp Johnson looks great and runs beautifully, although she is getting cranky in her old age.