Radical suggestion of how you link the offline catalogue on the tablets to the online system. You could put QR codes on the site of each of the items, then scan it with a webcam to send your sales computer to the right item on the online shop.
Perhaps a bit overly convoluted, but that way you could essentially have all of your purchases run through your online store, whether they're in store or not.
Would it not be hugely easier, cheaper and more reliable to use NFC chips?
Wouldn't have thought so.
QR is license-free, NFC isn't. NFC is pretty expensive, all you need for QQR, once you've designed it, is a printer and some printer label sheets, if you want to put it on the products themselves. But that wasn't what I was suggesting (but is a nice idea too).
I was trying to think of a way in which you can link an offline and online catalogue together, so if the tablet is offline, and a customer has selected something, how do they get it/pay for it? NFC isn't really that useful in that situation, instead, if you have a webcam that scans the relevant QR code on the catalogue entry saved on the tablet. It could then access the particular part in the catalogue on the online account, where the transaction can be processed. Would mean he has one central DB for both online and offline tranactions. Of course, if he also used QR labels to replace barcodes, with the webcam, that would effectively act like a scanner for the 'barcode'.
Might be hassle creating every QR code, for every entry, and possibly overengineering it, but it's just an idea. NFC tags seem to me, to be totally overengineering it. NFC simply isn't really at the races yet, IMO. And that's from someone who designs and sells NFC kit...
The difficulty is preventing it from being shut down or the browser closed - to some how lock it until I shut it down for the night...
If you use an android tab you could knock up an home-screen replacement app quite simply that would run in a kind of pseudo-kiosk mode. As long as it had wake-lock permission it could keep the device on indefinitely.