Originally Posted by axxiom
Isn't he right? "one per purchase" sounds to me like "one per transaction".
"One per purchase [of item(s) specified]" is the usual wording. Manufacturer means you can't use 2 coupons on your purchase of 1 item X.
One per transaction means you can use one coupon for item X in your whole transaction, regardless of the number of items X you buy.