Is it permissible, Islamically, to purchase a piece of land at a price approximately 50% higher through installments, via a person who buys it with cash and then sells it to me, knowing that I wish to buy it for commercial purposes and do not possess its cash value?

The transaction mentioned is a Murabaha sale. Its permissibility is conditioned upon the fulfillment of the legitimate Murabaha ضوابط (Islamic legal requirements), such as the person truly owning the land, the land entering into their guarantee (responsibility), and then selling it afterwards without a prior obligation on the buyer to purchase it from them. If these ضوابط are met, the transaction is permissible with any agreed-upon profit; otherwise, it is not.