$customer=mysqli_real_escape_string($db, $_POST['user']);
$query = "SELECT * FROM `products` WHERE `customers` = '$customer'";

FORM metod post
customer, brand, model, price, date between to date

$from=mysqli_real_escape_string($db, $_POST['date1']);
$to=mysqli_real_escape_string($db, $_POST['date2']);
$customer=mysqli_real_escape_string($db, $_POST['user']);
$model=mysqli_real_escape_string($db, $_POST['getmodel']);
$price=mysqli_real_escape_string($db, $_POST['getprice']);

$query = "SELECT * FROM `products` WHERE `customers` = '$customer' and `from` = '$from' and `to` = '$to' and `brand` = '$brand' and `model` = '$model' and `price` = '$price'";