Is it permissible to purchase a discount voucher for a certain amount to benefit from a larger discount on a particular item, given that there is no gharar (excessive uncertainty/deception) involved?

The ruling on coupons sold by some intermediary companies between the customer and the seller is prohibition (haram). The claim that there is no gharar (excessive uncertainty/risk) in this is not accepted, because gharar is present due to the possibility of purchase or non-purchase.