All perfect praise be to Allah the Lord of the Worlds. May His blessings and peace be upon Prophet Mohammad and upon all his family and companions.
Amongst the conditions of the sale transaction, according to jurists, is that the commodity should be settled in the possession of the seller before concluding the contract of sale. It is stated in [Moghni al-Mohtaaj, v.2: pp.349]: "In the sale transaction, it is conditioned that the commodity is possessed by the seller based on the Hadith: "There is no sale transaction till you possess." {Related by At-Tirmith}.
It isn`t permissible for the employees of the above company to sell the coupons before they actually take possession of the products to be exchanged with these coupons because they are a gift and a gift is possessed once it is received. For more details, kindly check Moghni al-Mohtaaj, V.3:P.565 by al-Shirbini.
Moreover, this sale transaction involves a great deal of ignorance (Jahalah) since neither the seller knows what he is selling nor the buyer knows what he is buying, and it is no secret that ignorance invalidates a contract of sale.
Prohibiting the sale of such coupons is further supported by what Imam Malik mentioned in his book "Al-Mowatta`." He said that at the time of Marwan Bin al-Hakam similar coupons were distributed amongst the people and they started selling them before actually taking possession of the products represented by the coupons. Therefore, Zaid Bin Thabit and one of the companions of the Prophet (PBUH) went to Marwan and said to him: "How dare you permit the sale of usury?!" he replied: "How so?!" they said , "The people have sold the coupons before taking possession of the products to be exchanged with them."
In conclusion, if the employee took possession of the products-represented in the coupon-then he is permitted to sell them for whatever price he wants. And Allah the Almighty knows best.