You can use your constructor for creation a new object and define its properties by default (include getting dbh, because I think you will store new tickets in the database):

our $properties = { time            => undef,
                   trad_ref        => undef,
                   adr_buyer_bank  => 'test',
                   adr_seller_bank => undef,
                   seller_pays     => undef,                   
                 };
sub new {
    my $class = shift;
    my $self = {};
    map { $self->{$_} = $properties->{$_} } keys %$properties;
    bless $self, $class;
    $self->_init(@_);
    return $self;
}

sub _init {
    my $self = shift;
    if(@_) {
        my %args = @_;    
        map { $self->{$_} = $args{$_} if exists $self->{$_} } keys %ar
+gs;
    }

    $self->{__dbh} = DBI->connection(...) unless defined $self->{__dbh
+};
}

sub load {
    my $self = shift;
  
    my $sql = "SELECT * FROM tickets WHERE id = ?";
    my $sth = $dbh->prepare($sql) or die $dbh->errstr;
    $sth->execute($ticket_number);
    my $row = $sth->fetchrow_hashref;
    
    $self->_init(%$row);
    
    return 1; 
}
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Use its in the script or another module:

my $ticket = MyApp::Ticket->new();
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or using input parameters:

my $ticket = MyApp::Ticket->new(time            => time(),
                                trad_ref        => 34567,
                                adr_buyer_bank  => 'blah',
                                adr_seller_bank => 'blah,
                                seller_pays     => 99.99);
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For load existing ticket use method load, as you wrote:

my $ticket = MyApp::Ticket->new();
my $res = $ticket->load(12345);
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It's just rough but idea is you need only one constructor and others are methods. Of course, I didn't implement errors catch but it's another story.

      
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SV* sv_bless(SV* sv, HV* stash);