Is it permissible to back out of a verbal agreement to sell a house, for which the price has not yet been paid, given that the seller stipulated the relocation of the pharmacy located in the house, and no deadline was specified for this? And if backing out is forbidden, what is its expiation?

If the sale contract is concluded with offer and acceptance, then the contract is valid, and the ownership of the house transfers to the buyer and the price to the seller. It is not permissible to revoke it except with the buyer's consent. The non-receipt of the price or the non-documentation of the contract does not affect its validity. The contract must be fulfilled, in accordance with the Almighty's saying: "O YOU WHO HAVE BELIEVED, FULFILL [YOUR] CONTRACTS." However, if the matter is merely a promise to sell, it is permissible to retract it for a valid excuse; otherwise, it is obligatory to fulfill it religiously and judicially, especially if the promise resulted in a cost to the other party. The obligation is to fulfill the promise or compensate the injured party.