Back in the 1990s Sainsburys (a UK Supermarket) had a version of self checkout where you had special trolleys and big boxes you took home and put in your car an

Back in the 1990s Sainsburys (a UK Supermarket) had a version of self checkout where you had special trolleys and big boxes you took home and put in your car and a hand scanner you walked around and scanned items with. You then took that to a till designated for it and they had an algorithm for when to rescan people. The idea people most of the time till time was very short and it was just payment. Usually people got checked on the first few goes and if items were found that hadn't been scanned then more rescans would appear in the future. It was meant to drop down to about 1 in 20 for rescan. Within about a year the entire thing collapsed. Almost everyone was caught stealing expensive stuff like nappies and especially alcohol and the algorithm had the system rescanning almost everyone everytime and rescans took longer than people just putting the items on the conveyor belt. The few people who used it honestly found themselves in long queues behind people who stole due to the rescans and the attempt to save supermarket labour ended up costing much more. Given that happened it amazes me we have the self checkout systems we do now. There is an obvious and clear trade off where people will use self checkout to take items without paying for them however you choose to organise it. As a business they have to decide if those loses pay off compared to the staff cost.