Gui keeps copying?

The line:-

if not player.PlayerGui:FindFirstChild(guiClone)then

Try's to use the object guiClone and not the name of the gui

Simply add Name:-

function onTouched(hit)
    if hit.Parent:findFirstChild("Humanoid") then
        local player = game.Players:GetPlayerFromCharacter(hit.Parent)
        local gui = game.ServerStorage.PerkShop
        local guiClone = gui:clone()
        if not player.PlayerGui:FindFirstChild(guiClone.Name)then
        guiClone.Parent = player.PlayerGui
        end
    end
end

script.Parent.Touched:connect(onTouched)

This is because the method FindFirstChild will not convert the object into a string so the result will be nil allowing for duplicates.