// validate editable fields
$editable_fields = array("customerid"=>"is_int",
                         "project"=>"is_string",
                         "fixedquote"=>"is_string",
                         "quoteamount"=>"is_numeric",
                         "quotehours"=>"is_int",
                         "active"=>"is_int");

// is it an editable field?
if (isset($editable_fields[$_POST['field']])) {
    // is the value valid?
    if (eval("return ".$editable_fields[$_POST['field']]."('".addslashes($_POST['value'])."');")) {
        /* ... do stuff ... */
    } else {
        /* error about not being the right type of data */
    }
} else {
    /* error about not being an editable field */
}