On each page there should be back and forward arrows through items, customers, invoices, etc.
If I have to make changes to each item (or just view a list of items/invoices/customers), I currently have to open the item, make the change, save it, go back and find the next item, repeat.
If there were previous and next arrows between the chosen products/invoices/customers etc it would simplify things.

There should be links to the item page from invoices, tickets and repair bundles.
- So if I notice an error (price, spelling etc) I can simply click on the item to open its page and make the change, rather than having to go to inventory, search for the item, make the change, then go back to where I was.