Once per day, the player can win a random prize from the raffle. Unlike other shops, the Raffle Shop's merchandise pool doesn't increase as it levels. Instead, the player's chance of getting a top prize is increased.
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Raffle Shop prizes
First place: Master Ball
Second place: Rare Candy
Third place: PP Max
Fourth place: PP Up
Fifth place: Max Revive
Sixth place: Max Elixir
Seventh place: Max Ether
Eighth place: Ultra Ball
Ninth place: Full Heal
Tenth place: Berry Juice
Source: Bulbapedia's page on Join Avenue.