In this age of barcodes, most supermarkets have a block on buying more than two packets, or products in the same transaction. I guess this at least bring's it to the attention of "Johnny or Jenny No Stars" manning the check-out. I was once caught out buying two packets of co-codamol and some "cold and Flu" tablets that also contained paracetamol. I guess as I didn't look like a suicide risk, and wasn't attempting to buy forty packets, the check-out girl just let me put them through as a separate transaction? As a rule, perhaps they shouldn't?