Hi brazorf,
The solution of your problem is you need to goto the directory path
components/com_jsautoz/views/seller/tmpl/formvehicle.php
in this file search for the code
case 'checkbox':
echo '<input type="checkbox" name="userfields_'.$k.'" id="userfields_'.$k.'_field" value="1" '. 'checked="checked"' .'/>';
break;
and replace the above code with the following once
case 'checkbox':
$check = ($fvalue == 1) ? 'checked="checked"': '';
echo '<input type="checkbox" name="userfields_'.$k.'" id="userfields_'.$k.'_field" value="1" '.$check.'/>';
break;