If a buyer defaults on a contract to purchase, the seller may do which of the following to enforce the contract

Filing a lien on the buyer's home would not directly enforce the original contract for purchase. A lien is typically a claim against property to secure payment of a debt, and while it may provide the seller a way to recover money owed, it does not compel the buyer to proceed with the purchase of the property in question.

An injunction is a court order that requires a party to do or refrain from doing specific acts. However, obtaining an injunction to prevent the buyer from purchasing another home does not address the original contract's enforcement. It would not compel the buyer to fulfill their obligations under the contract for the specific property in question.

Suing for substantial performance is not applicable in this context, as it pertains to contracts where a party has completed most of the contractual obligations but has not fully complied. In real estate, the seller typically seeks specific performance to enforce the contract, not substantial performance, which is more relevant in construction or service contracts.