Question Author
Thanks for the answers.
However, I don't believe this is theft. After I had given them the invoice I had for the goods, which clearly showed an amount outstanding, they loaded the goods into my car and said goodbye. Is this not arguably an implicit acceptance of them accepting a reduced amount as payment? Contract law experts? In my mind it is certainly not 'theft'.
Furthermore, I believe the onus isn't on me to prove I paid - its on them to prove I didn't. For example, if requested at some subsequent point, how would anyone be able to *prove* a cash payment - as an individual I'm not legally obliged to keep any receipt or records of having made a payment.
Also, I don't think I fully explained the significance (at least to me), of spending 10 minutes outside the shop with an employee. They could not *prove* that during this time I hadn't settled the balance by cash with the employee conderned. This is not to say I would outright lie if asked, thus placing the employee under suspicion of theft, but that the shop would have to (or should) consider such things if and when it was weighing up whether it could successfully pursue me for the balance.
Finally, their IT and accounting systems may well show that the payment hadn't been entered onto the system, giving an outstanding balance. However, this doesn't *prove* that I didn't make any payment; accounting errors do happen. An outstanding balance on the accounting system may *suggest* payment has not been received, but does not *prove* it. At least not to a degree sufficient for a small claims court to find against me. From my knowledge of accounting systems, there are a number of other potential reasons for the balance to be shown incorrectly.