You want to buy Der Professor? You want it at a lower price? Or do you just not have the possibility to pay with PayPal or a credit card? No Problem! Der Professor is now listed on g2a.com. g2a.com is a key store that is similar in structure to ebay. But here you can buy everything immediately. Various users, including you, can offer different keys for sale. G2a.com offers more payment methods than Desura.
https://www.g2a.com/der-professor-supporter-edition-desura-cd-key-global.html
But beware! We have nothing to do with the sale of this product key. However, we recommend the Official route via Desura! It is just a tip for user who can not pay via Paypal or credit card!
