Wal-mart
Cashier, store supervisor, and manager walmart's in-store checkout system triple charged my credit card (around $300 instead of $90)
When Wal-Mart initially installed the self-checkout, they had staff standing by to help the customers (until they would work out the quirks in their new system). I ran my card once. The clerk had to come over to help, as they were having to help with many of the customers who were checking out at ...