Shop not taking my money when bought an item?

Hello, It's because your code is client sided, the server changes your money back to it's original form. To fix this you'll need to make it server-sided by using RemoteEvents

Here you go I made an example for you :

LocalScript

local price = script.Parent.Parent.Price 
local tools = game.ReplicatedStorage:WaitForChild("Library")
local tool = script.Parent.Parent.ItemName 
local player = script.Parent.Parent.Parent.Parent.Parent.Parent

script.Parent.MouseButton1Click:connect(function() 
    if player.leaderstats:FindFirstChild("Cash").Value >= price.Value then   
        game:GetService("ReplicatedStorage").RemoteEvent:Fire(price.Value,tool.Value)
    end
end)

ServerScript

local Remote = Instance.new("RemoteEvent",game:GetSerivce("ReplicatedStorage"))
local tools = game.ReplicatedStorage:WaitForChild("Library")

Remote.OnServerEvent:Connect(function(player,price,tool)
    local usercash = player.leaderstats:FindFirstChild("Cash")
    if usercash.Value >= price then
        usercash.Value = usercash.Value - price
        tools[tool]:Clone().Parent = player.Backpack
    end  
end)

Feel free to comment if there's any bugs or you need more help.