Hi, my name is Lucas, I have been developing Unity and iPhone projects for almost five years for a big company located in California. My contract is now over, because they no longer hire external developers, so I started developing projects as a freelancer.
I don't know exactly what application you are looking for, but I have already designed and coded in Xamarin a mobile app for iPhone and Android, and also started but not finished for WP8. The application scans barcodes from products (in my app they are books, but they can be whatever you want), and search the code via a web service, and show you the product detail. You can also search for products, and add the products to a cart. The app can register and login users, and also has a map with your location and stores near you. It only lacks the buy option, but I can make it redirect the user to your (or any) web site to complete the payment.
I can sell you the code as is (app, web service and db), can also help you running it and customizing the type of products you will need, and then we can arrange for further improvements or modifications.
Feel free to contact me for more details.
Regards,
Lucas: