As a participant in the Shop Hops every month - I can provide some information about the prize coupons/gift certificates.
a) They are NOT TRANSFERABLE - unless the shop in question chooses to accept it, if the order name is different than the name on the coupon, the coupon will not be acceptable and the shop owner should contact you to determine what to do with the order.
b) They DO NOT cover shipping costs. Most of the shops in the hop are small enterprises and giving away free shipping on a small order adds a lot of expense to the prize. On a lot of stores though, they'll be applied after the store minimum free shipping threshold is met. Some not.
c) They DO have a limited life. Usually they must be used in a specific time period, normally within about 3-4 weeks of when they are issued.
Hope this helps clarify...