NIP-XX: NIP-99 Marketplace Listing Extension

[pats2sats]

Summary

Adds a generic marketplace extension for NIP-99 classified listings. The proposal defines shared listing tags and profile conventions that can be reused across marketplace verticals such as accommodation, vehicles, goods, rentals, and services.

What this defines

• Marketplace profile tags using t values.
• Generic listing tags for auto-acceptance, negotiability, rent-or-buy mode, duration limits, quantity, security deposit, minimum payment, maximum dispute period, and cancellation policy.
• Promoted tag conventions for relay-filterable fields.
• Guidance for profile-specific location encodings and client behavior.

Scope

This provides the generic listing layer. Profile-specific tags, such as accommodation features or other vertical-specific promoted tags, belong in separate profile specifications.