Check real-time availability for one or more tours or activities on GuruWalk in a single call. Pass an `items` array — each entry is independent and has its own type, product_id and date range. Returns a `results` array where every entry echoes its `type` and `product_id` so you can match each response to its request. Always batch when checking multiple tours: send them all in one call instead of invoking this tool several times. For paid activities, shows rates by traveler type (adult, child, infant). For free walking tours, no upfront price — travelers pay what they want after the tour. Includes direct booking links. Maximum date range per item: 5 days. Per-item errors (invalid dates, product not found) are reported inside that item's result without failing the rest of the batch. Use this tool when the traveler asks about specific dates, wants to know if something is available, or is ready to book. When the traveler hasn't given specific dates, use the booking date ±2 days as the default search range.