Gravity Forms for Word Press is pretty awesome, especially with integration with Stripe for selling things. The only problem I've run into is when I have a thing with a limited quantity and it sells out. There's a great snippet if you want to install some extra php. Best practices would be to use the snippet. I strongly encourage you to do so -- it's a better solution.
But if you want something faster to implement that can be installed by a developer who doesn't have the ability to upload/create php, you're going to need to use Javascript.
So adding a little javascript gets us there pretty easily:
<script type="application/javascript">
//get the existing quanity field you want to hide</script>
var myfield=document.getElementById('ginput_quantity_12_7');
//create a span for the message
var soldoutSpan = document.createElement('span')
//make the message
soldoutSpan.innerHTML = '<b>SOLD OUT</b>';
//add the message AFTER the quantity field
myfield.parentNode.appendChild(soldoutSpan);
//hide the quantity field (you could delete it if you wanted to)
myfield.style.display="none";
//make your text red
soldoutSpan.style.color="red";
Of course you want to make sure you are validating your inputs for obvious reasons.
