Quantum meruit is a Latin term meaning "as much as he has deserved." In contract law, it refers to a legal principle that allows a person to claim a reasonable amount of compensation for goods or services rendered even in the absence of a formal contract. It is commonly used when there is an implied contract or when the terms of the contract are unclear or incomplete.

Quantum meruit is an equitable relief given where the terms of a contract may not be enforceable but the party who has performed is awarded a reasonable value for the work performed by such party (which may be less than the expected contract rate).

No. If the neighbor never talked to you prior to fixing the fence, quantum meruit does not apply.

Yes.

Yes. A licensed contractor could claim a lien under the legal doctrine of quantum meruit. However, the lien will expire (in 8 mos. in WA) if not foreclosed. Your best option, if you are not selling or refinancing, is to do nothing.