Thanks for the recommendations!
Hopefully some of our users will be able to make some suggestions, but I just wanted to make you aware of a few options that may help.
We can integrate with Zapier. Zapier, if you're not aware, is basically a middle-man between two pieces of software. You can have a trigger in one package, which will perform an action in another. For example, when an invoice is created, it can perform an action in stock control software. There are limitations, but for a small retailer, it may work.
We have an XML and JSON API. If they have technical knowledge, they may want to look at developing something themselves which can potentially link any system to QuickFile (providing the other system has an 'output', like a webhook or an API). If they don't have the knowledge, we work with an agency who has experience with the QuickFile API, and may be able to help with this.
If you would like any further details on the above, please let me know.