We have a whole lot of suppliers which supply products, their prices and quantities to us in various different formats (i.e. XML, CSV, Excel, etc.) all of which are uniquely identified by their SKU codes.
I have put together a script which fetches all these products from the various mediums and then creates a local database of products. Each time the script is run, it identifies products which have changed (in price or qty).
The final step is to now update the prices and qty of these products in the shopify site/api, which is now proving to be a real headache :O