A guy once phoned me saying that he works for a private hospital X that would like to sell their unused/sealed original cartridges which they have no use for as the machines have been replaced. I negotiated a rock bottom price and the gentleman dropped them off and I paid cash. Then a few months later I got another call from the same guy wanting to sell the same cartridges again. It sounded a bit strange because I thought I bought all their unused cartridges last time. When I asked why they still have these cartridges he hesitated and said they discovered more in storage. At this point I got very suspicious. I told him that I just need a few days to get cash in and that I will phone him when I am ready. If I was a crook I would have just bought the dam things as I would be making a huge profit, anyway, I phoned the hospital and got through to a gentleman who I think was the hospital manager. I explained the situation to him and I told him that I had already sold the first batch of cartridges. I gave him the cartridge codes and the name and number of the guy in question. He told me that it does sound fishy and that he will investigate. He phoned me back a few days later and confirmed that the guy in question was confronted and confessed. I apologized for having bought the first batch and he told me not to worry and that he is extremely grateful that I brought this to his attention.
Since then I have been contacted by other people wanting to sell unused cartridges. I now go to the businesses and speak to the owner/manager to make sure it is legit. Most often it is legit, but one guy put the phone down when I said I want to come to his work to get the cartridges.
In a big business it is easy for somebody to steal them without you noticing it and just as easy to sell them. So guys lock your cartridges away and keep a good record of them.