What I am saying ainitatyb is that you would be in on the theft too - so they should let you leave the store. The checkout operator is also under suspicion, but they need to check the till receipt there and then whilst you are their to apprehend both parties. If it was done later the goods and yourself might have disappeared. A aquick way for them is to check transactions either randomly or every transaction to weed it out.
I don't think it is legal until you leave the store but this particular theft occurs at the till as the intention was never to pay for it because the till operator is in on it too.
I think someone should ask MAKRO next time it happens and I'd really be interested in their response.