I found this table on a Japanese manufacturer's website, but the grading system doesn't seem to be as uniform as that for diamonds. Other websites had similar tables, but not exactly the same.
AAA Exceptional, Mirror-Like Reflection Blemish-Free Surface*
AA Superb, Clear Reflection Very Slightly Blemished
A+ Very Good, Clear Reflection Very Slightly Blemished
A Good, Clear Reflection Very Slightly Blemished
A1 Good, Clear Reflection Slightly Blemished
Cultured pearls, freshwater pearls, Japanese pearls, South Sea pearls are all real, so it's really just a matter of what you like. Cultured pearls have a seed put into the shell, so the pearl is formed around it. They are generally the most regular-shaped.
Some people can tell the difference - I have a lovely Japanese Akoya pearl necklace and I wore it out to dinner once and one of DH's colleagues asked me why I wasn't wearing Australian pearls (we were living in Darwin at the time). I don't know how he could tell though.
Are you shopping online? Can we help you choose?
Did you tell him because australian pearls and massively overpriced and the conditions that pearl divers work in are criminal?
Op nothing to add from PPs comment - other than as long as they have a good rating and are pleasing to your eye don't worry where they come from just get the best price.