Hi there,
I'm Duncan, 29 and am currently working for a small company in London. I have been working there as their inhouse database developer for the last 6 years. I'm a Certified Filemaker Developer for versions 11-14.
Your project is very similar to a project I've just finished. The project I've just finished was to create an inventory, customer and sales system for an optician. To manage all the sales and inventory using a barcode scanner (On Iphone and Ipad as well as an actual barcode scanner)
I think this the same sort of system that you are looking for!
If you would like to see any of my previous work or have any other questions please feel free to contact me!
Kind regards,
Duncan