Avrei pensato a una cosa del genere come script, giusto per farvi capire come l'ho pensata, ma chiaramente non funziona.

codice:
<?
$user = 'USERNAME';
$pass = 'PASSWORD';
$postdata = "username=" . $user . "&password=" . $pass;


$ckfile = tempnam ("C:/Users/Sviluppo/AppData/Local/Temp/", 'cookie');




$request  = curl_init();
curl_setopt_array($request, Array(
    CURLOPT_URL => 'https://www.amazon.it/pagina-con-pulsante-contatta-il-venditore/etc.....',
    CURLOPT_SSL_VERIFYPEER => false,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_FOLLOWLOCATION => false,
    CURLOPT_COOKIEJAR => $ckfile,
    CURLOPT_TIMEOUT => 30,
    CURLOPT_USERAGENT => "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.124 Safari/537.36",
    CURLOPT_HEADER => true,
    CURLINFO_HEADER_OUT > true,
    CURLOPT_CUSTOMREQUEST => "POST",
    CURLOPT_POST => true,
    CURLOPT_POSTFIELDS => $postdata
));
$response = curl_exec($request);
curl_close($request);






$request2  = curl_init();
curl_setopt_array($request2, Array(
    CURLOPT_URL => 'https://www.amazon.it/pagina-con-form-invia-richiesta-al-venditore/etc.....',
    CURLOPT_SSL_VERIFYPEER => false,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_FOLLOWLOCATION => false,
    CURLOPT_COOKIEFILE => $ckfile,
    CURLOPT_TIMEOUT => 30,
    CURLOPT_USERAGENT => "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.124 Safari/537.36",
    CURLOPT_HEADER => true,
    CURLINFO_HEADER_OUT > true
));
$response2 = curl_exec($request2);
curl_close($request2);
?>