There is a simple Inventory Template included with current versions of Filemaker.
It is not related to a Customers Database, and would have to be customized.
Starting Point has a Products module in it and is a free template, although complex to modify.
No inventory module, but worth looking at - free template
I saw that and it didn't help - saw the page, didn't see where to download the file.
Then I noticed a business productivity download on Filemaker's site and - voila! - guess what a major part of that system is?
So I have been working with the Business Productivity Solution from Filemaker and it's essentially awful. There are no explanations, the system is complicated, and it essentially sucks.
You would think I wouldn't be the only guy who needs a system to track sales and inventory thereof, but I have yet to find anything that really works.
Seriously, this can't be the case.