As someone who once worked in a "loss reduction" department, I can say the most likely reason they are taught to turn the carousal away from the customer is to keep unscrupulous customers from slipping unpaid merchandise into the bags with other product that has been already scanned. Having shoplifters either "co-mingle" paid and un-paid merchandise in a single bag or just brazenly put product into a bag and try to walk out was a fairly common problem. From the thief's perspective, co-mingling the product is a good strategy. First, since they are buying stuff, it is less suspicious, but also if there is a receipt checker, he may not notice the unpaid product or if it does get caught, the thief can claim that it was the checker who did not scan the product.
