A maintainable website uses recognizable project structure, clear configuration, documented dependencies, ordinary deployment patterns, and business-named abstractions so another competent developer can take over later.
A proper website handoff should give the owner access, ownership records, backups, concise documentation, renewal information, and a realistic maintenance path rather than a single login and no context.
A small-business website handoff should document the few systems, accounts, renewal responsibilities, deployment steps, backups, and recovery paths needed for the owner or another developer to take over.