Backdrop: Am building a shopify app using a test store provided by shopify. #Python #Django-
Problem: I have setup shopify webhooks for my test store using the python API for the topics "products/update" and "products/delete". But my endpoints are not called by shopify when I manually update or delete a product on my test store.
My detective work so far: I have checked the following:

I have confirmed that the webhooks were successfully created using the API. I simply listed all the existing webhooks using the API for the store and mine are there.
The address/URL I specified in the webhook for shopify to call in the event of a product update or delete is a public url, as in it is not on my localhost. (not 127.0.0.1:8000 etc.)
My webhook endpoint is fine. When I manually call my endpoint in a test case, it does what it should.
I contacted the shopify apps support guys, and I was asked to post this issue here.

Another minor issue is that I cannot find in the shopify API docs exactly what JSON/XML the webhook will POST to my URL in the event it should. So I do not know what that JSON will look like...
Any help would be appreciated!
I don't have the creds to comment apparently, so I'll put this in an "answer" - to use the term very loosely - instead. I ran into something similar with the Python API, but soon realized that I was doing it wrong. In my case, it was toggling the fulfillment status, which then fires off an email notifying customers of a download location for media. 
What I was doing wrong was this: I was modifying the fulfillment attribute of the order object directly. Instead, the correct method was to fetch / create a fulfillment object, modify that, point the order attribute to this object, than save() it. This worked.
I don't know if this is your issue as there's no code posted, but I hope this helps.
--Matt
Shopify webhook not working when product updated/deleted