Is it permissible to donate $70 on behalf of a non-Muslim person who was defrauded and not paid his due for something displeasing to Allah, with the intention of expiating a sin and redressing an injustice?

If the item sold is unlawful, has no permissible benefit, and its sale or purchase is forbidden, then its price is not lawful for the seller, nor does he own it. Consequently, the seller has no right to this price, and the buyer is not obligated to pay it. If the buyer does pay it, the seller does not own it, and he must dispose of it by spending it on the poor or on public welfare. If the buyer receives and consumes the unlawful item, he must donate the price to the needy.