Is it permissible for a computer software marketer to offer customers a discount from his commission to attract them to purchase, or to display discount codes provided by the original seller or from his commission on his own website?

Marketing commission (brokerage fee or recompense) is permissible, and it is permissible for it to be a percentage of sales. There is no objection to marketing programs with or without a discount, provided that the original seller gives permission, and that the price of the programs and the marketing commission are known. There is no objection to placing the discount on your own website if the transaction is directly between you and the original seller.