you can not overtender credit cards in 8.52 because credit card companys charge a different rate (21% per day) for cash advances rather that regular purchaces (6% APR). this is why over tendering credit cards is not allowed. so what all used to do in old versions is ring the 3 items and then overtender the credit card and then give back store credit. Since Overtendering the credit card is no longer allowed this does not work. if you ring the items and then try to ring -100 for the SC the SC is not available if you have the check SC option in system prefs beacsue the balance on the invoice total is positive and it will not allow a 0 balance SC customer to use SC on this invoice. If you turn off the switch to check SC availabity then it works but now you have the issue of people using SC who do not have one. the answer to Als issue was to with no items on the invoice put the -100 and choose SC. since the balance of the invoice is 0 it will work and allow you to choose change SC 100 then choose the back button and list the items and then go back to tender and now the items are listed with the prepayment of SC.
in answer book under over tendering credit cards.