if ($(this).is(':checkbox') {
    //comprobar la clase del checkbox para saber que datos enviar
    if ($(this).attr('class') == 'filter1') {
        var filtro1 = $(this).val();
    }
    if ($(this).attr('class') == 'filter2') {
        var filtro2 = $(this).val();
    }
    if ($(this).attr('class') == 'filter3') {
        var filtro3 = $(this).val();
    }
}

$list = array('use', 'type', 'status', 'bhk', 'baths', 'size', 'location', 'price', 'description');
foreach($list as $name) {
    if ($name != 'description')
        $var = "\$" . $name . "=filter_input(INPUT_POST, '" . $name . "', FILTER_SANITIZE_NUMBER_INT);";
    else if ($name == 'description')
        $var = "\$" . $name . "=filter_input(INPUT_POST, '" . $name . "', FILTER_SANITIZE_STRING);";
    eval($var);  // que nadie use esto lol
}
 
$area_1 = $size['area1'] != '' ? $size['area1'] : 0;
$area_2 = $size['area2'] != '' ? $size['area2'] : 0;
$city   = $location['city'];
$zone   = $location['zone'];
$sale   = $price['sale'] != '' ? $price['sale'] : 0;
$rent   = $price['rent'] != '' ? $price['rent'] : 0;
 

if ($stmt = $mysqli->prepare('INSERT INTO property (use, type, status, bhk, baths, area_1, area_2, city, zone, sale_price, monthly_price, description) VALUES ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?')) {
    $stmt->bind_param('iiiiiiiiiiis', $use, $type, $status, $bhk, $baths, $area1, $area2, $city, $zone, $sale, $rent, $description);
    $stmt->execute();
 
    $id = $mysqli->insert_id;
 
    if ($sale != 0) {
        if ($stmt = $mysqli->prepare('INSERT INTO for_sale VALUES ?')) {
            $stmt->bind_param('i', $id);
            $stmt->execute();
        }
    }
 
    if ($rent != 0) {
        if ($stmt = $mysqli->prepare('INSERT INTO for_rent VALUES ?')) {
            $stmt->bind_param('i', $id);
            $stmt->execute();
        }
    }
} else echo "Statement failed: " . $mysqli->error . "<br>";

<ul>
    <li style="margin-top: 9px;">
        <input type="checkbox" id="price1" value="">
        <label for="price1"><span></span>Se Vende</label>
    </li>
    <li class="price-1" style="display: none;">
        <input type="text" placeholder="Precio de Venta" name="price[sale]" /> <span class="unit unit-2">&euro;</span>
 
    </li>
    <li class="test">
        <input type="checkbox" id="price2" value="">
        <label for="price2"><span></span>Se Alquila</label>
    </li>
    <li class="price-2" style="display: none;">
        <input type="text" placeholder="Precio de Alquiler" name="price[rent]" /> <span class="unit unit-2">&euro;</span>
 
    </li>
</ul>

_this.hiddenFileInput.setAttribute("name", "file[]");

<input class="dz-hidden-input" type="file" name="file[]" multiple="multiple" accept="image/*" style="visibility: hidden; position: absolute; top: 0px; left: 0px; height: 0px; width: 0px;">

$file_count = count($_FILES['file']['name']);
echo $file_count;

Dropzone.options.myAwesomeDropzone = {
    url: 'upload.php',
    paramName: "file",
    acceptedFiles: 'image/*',
    addRemoveLinks: true,
    parallelUploads: 6,
    maxFilesize: 6,
    maxFiles: 6,
    autoDiscover: false,
    autoProcessQueue: false,
    uploadMultiple: true,
    hiddenInputContainer: '#inputFile',
 
    init: function () {
        thisDropzone = this;
        thisDropzone.on("maxfilesexceeded", function(file) { thisDropzone.removeFile(file); });
    }
};

    $('.click').click(function() {
 
        if ($('#res_prop').is(':checked')) {
            var prop_type = $('#res_prop').val();
        }
        else if ($('#com_prop').is(':checked')) {
            var prop_type = $('#com_prop').val();
        }
 
        $.ajax({
            method: "POST",
            url: "/search",
            data: {
                prop_type: prop_type,
                city: $('select[name=city]').val(),
                zone: $('select[name=zone]').val(),
            }
        }).done(function(data) {
            $('.cont-1').hide();
            $('.cont-2').show();
        });
 
        return false;
    });