Senior
Let fans pick exact seats, hold them while they pay, and never sell one seat twice.
Build the booking system behind a ticketing site for concerts and sports. Fans open an event, see the venue's seat map with the seats still free, and pick the exact seats they want. They then have ten minutes to pay while no one else can take those seats; if they don't pay in time, the seats go back on sale. Payment goes through an outside card processor, and once it succeeds the fan gets their tickets. A seat must never be sold to two fans.
Most days, traffic is steady. But when a popular artist's tour goes on sale, tickets are released at a set time and far more fans arrive in the first minutes than there are seats, all trying to grab the best ones at once.