What are the types of non guaranteed reservation system?

Non-guaranteed reservation systems typically include types such as "tentative bookings," where customers hold a reservation without a deposit, and "courtesy holds," allowing potential guests to reserve a room for a short period without commitment. Additionally, "waitlist reservations" enable customers to express interest in fully booked accommodations, while "last-minute bookings" often allow for flexible arrangements without guarantees. These systems rely on customer trust and may lead to overbooking or cancellations.