How do you make it so that you can only buy one on the same item in the shop?

local player = game.Players.LocalPlayer
local leaderboard = player:WaitForChild("leaderstats")
local button = script.Parent
local price = button:WaitForChild ("Price")
local item = button:WaitForChild ("ItemName")
local rs = game:GetService ("ReplicatedStorage")

found = false
if player.Backpack:FindFirstChild('Normal Key') then
	found = true
end

button.MouseButton1Click:connect(function()
	if leaderboard.Money.Value >= price.Value and found == false then
		leaderboard.Money.Value = leaderboard.Money.Value - price.Value
		local item = rs:WaitForChild(item.Value)
		item:Clone().Parent = player.StarterGear
		item:Clone().Parent = player.Backpack
	end
end)

You should change your code to like this:

button.MouseButton1Click:connect(function()
if player.Backpack:FindFirstChild('Normal Key') and leaderboard.Money.Value >= price.Value 
then
	leaderboard.Money.Value = leaderboard.Money.Value - price.Value
	local item = rs:WaitForChild(item.Value)
	item:Clone().Parent = player.StarterGear
	item:Clone().Parent = player.Backpack
else
	button.Text = You already have this item!
end
end)

That's should be the code, make sure then is on the same line as the if statement.