POS Maid Software CAN I DELETE A SALE ?

You can not delete sales because in most of the countries this kind of a system would be illegal if it could delete sales, because people would be able to very easily hide taxes from the government without any trails.  If this was just a trial of the software (phony sale), I would suggest to just reinstall the software and starting all over again. Otherwise, you must REFUND sales that have been entered by a mistake or need to be removed for other reasons.