cut -f3 -d, <file1.csv | sort -u >file1.cut.sort
cut -f3 -d, <file2.csv | sort -u >file2.cut.sort
comm -23 file1.cut.sort file2.cut.sort
##</code><code>##

use strict;
use warnings;
my $file2 = {};
open my $fh2, "<file2.csv";
while( <$fh2> ) {
    chomp;
    my @fld = split /\,/;
    $file2 -> { $fld[2] } = 1;
}
close $fh2;
open my $fh1 "<file1.csv";
while( <$fh1> _ ) {
   chomp;
   my @fld = split /\,/;
   defined( $file2 -> { $fld[2] } ) and next;
   print "$_\n";
}
close $fh1;