Earlier quoted context omitted.
…which is easy enough to fix with bar codes. This is how it works in Germany. You pay a deposit on every bottle. To get your money back requires a machine to recognise each bottle/can as legitimate, based on the bar code. Now, yes, people could print stickers with fake bar codes on… but I don’t think that would work well at the scale of the major fraud operation you’re envisaging…
Do they use a different bar code on bottles sold in Germany to those sold by the same producer in bordering countries? That's something American producers generally don't do for different states (yet?) - they use the same label and write the relevant deposit amount for every state on the bottle.
You cannot get cash from foreign cans or PET bottles, since the deposit was not paid here.
[1]: https://en.m.wikipedia.org/wiki/International_Article_Number