What is the ruling on borrowing paid theoretical driving exam sample questions from a neighbor, and is it obligatory to inquire about their source to pay their price, or to buy new samples? What is the value of the subscription that must be paid? And is the seller's promise to buy from him a second time without fulfilling it considered an injustice?

If the source of the samples obtained by the neighbor is unknown, there is no need to inquire about their origin, because the default assumption for a Muslim is safety and soundness. What is unknown among hidden matters is considered non-existent.

It is permissible to deal with all the wealth in the possession of Muslims and People of the Book, unless it is known through evidence or indication that it was usurped.

Bargaining is permissible. If a sale is concluded based on a promise from the buyer to purchase again, he should fulfill his promise. Fulfilling the promise becomes obligatory if the promise led the seller to accept the price and he would be harmed by its retraction; otherwise, fulfilling it is a highly recommended act.