How can I detect clicks while using a mousehoverenter function? (GUI shop issue)

Hi guys,

I'm trying to make a system of buying a plot of land by using a screen gui which appears when the players mouse enters the boundary of a sign:

local sign = script.Parent


local function display_master(player)
    local mouse = player:GetMouse()

    local screengui = player:FindFirstChild("PlayerGui"):WaitForChild("buy_house")
        local master = screengui:FindFirstChild("m_frame")

    game:GetService("RunService").RenderStepped:connect( function()
        local Xpos = mouse.X
        local Ypos = mouse.Y

        if mouse.Target then
            if mouse.Target == sign
                then master.Visible = true
                master.Position = UDim2.new(0,Xpos,0,Ypos)
                --Here
            else master.Visible = false
            end
        end
    end)
end


sign.ClickDetector.MouseHoverEnter:Connect(display_master)

which works fine... however I want to make it so that when the player clicks (showing intention to buy) the current gui (which is displaying cost information) will disappear and another gui (pretty much saying "are you sure") will appear in it's place... I've tied this by using sign.ClickDetector:MouseClick:Connect() where the comment "here" is, but i don't think this is the best idea (I've also had issues with events firing more than once if the mouse leaves and then re-enters the frame. Is there a way to stop this from happening?)

Does anybody know how I should go about creating this system or how I should be detecting clicks?

Thanks for the help guys, I'm pretty new to this so sorry if im not clearly explaining my problem...