Car shop GUI Buy button not working?[SOLVED]

Like what aquathorn321 said. You need to make joints. However how he did it is incorrect. MakeJoints is a function, therefore you do not use MakeJoints like this: part.MakeJoints() but like this: part:MakeJoints. You also did this in your script.

player = script.Parent.Parent.Parent.Parent.Parent
cost = 5000

script.Parent.MouseButton1Click:connect(function()
     leaderstats = player:FindFirstChild("leaderstats")
    if leaderstats then
         money = leaderstats:FindFirstChild("Money")
        if money then
            if money.Value >= cost then
                spawncar = game.Lighting:FindFirstChild("CiviCar"):clone() --Use FindFirstChild or WaitForChild instead.
        local weld = Instance.new("Weld", spawncar.Seat) --Change this to any part in the car with a unique name. If your car already has welds, remove this line!
                spawncar.Parent = workspace
                spawncar:MakeJoints() --You need welds to actually use :MakeJoints(). MakeJoints is a function! Use ":" instead of "." like as if it's a property!
                player.leaderstats.Money.Value = player.leaderstats.Money.Value - 5000
                script.Parent.Text = "Bought"
                else
                script.Parent.FontSize = 14
                script.Parent.Text = "Not enough $"
                return
            end
        end
    end
end)

Hope it helps!

If it crumbles, then the problem is with the joints, therefore you should look over the piece of the code where you establish the joints. Line 12 reads spawn.MakeJoints() when it should read spawncar:MakeJoints().

Finished Script

local player = game.Players.LocalPlayer --Assuming the script is a localscript, you can shorten this.
local cost = 5000

script.Parent.MouseButton1Click:connect(function()
local leaderstats = player:FindFirstChild("leaderstats") --You don't need nearly as many if statements as you had, since if the code results in error, it will stop running and can be recalled when the button is pressed again.
local money = leaderstats:FindFirstChild("Money")
if money.Value >= cost then
local spawncar = game.Lighting["CiviCar"]:clone()
spawncar.Parent = workspace
spawncar:MakeJoints() --Assuming you already have proper welds established in the car.
money.Value = money.Value - 5000
script.Parent.Text = "Bought"
else
script.Parent.FontSize = 14
script.Parent.Text = "Not enough $"
end
end)