Cash value fails to update?

local cash = game.StarterGui.ScreenGui.cash.cashv

The issue is probably there. Correct me if I am wrong, but you are trying to update the value of a textlabel inside the PlayerGUI. What you've done wrong there is update it inside the StarterGUI, which is what players spawn with when they join the game.

EDIT: Didn't realise you could edit an answer, but oh well here's the instructions for fixing your issues.

Change the name of the value in the TextLabel to ' cashv ' (excluding the quotation marks) That was one factor in why it didn't work for you.

Ensure there is bread in ServerStorage Because the bread wasn't in ServerStorage, the script stopped there and didn't continue after that. I managed to avoid this by making the lines with the bread into comments.

Replace the script inside the dialog of the merchant to this: The only change are is in Line 8 where I moved the local for the variable into the event caller, and where I made it so that it would change for the player rather than inside the StarterGUI.

local merchantdialouge = workspace.Merchant.Head.Dialog:GetChildren()
local Bread = game.ServerStorage.Bread
local dialog = script.Parent


dialog.DialogChoiceSelected:connect(function(player, choice)
    if choice == script.Parent.buybread then
        local cash = player.PlayerGui.ScreenGui.TextLabel.cashv
        if cash.Value >= 5 then -- 5 is the amount of gold you need to purchase bread       
            game.ServerStorage.Bread:clone().Parent = player.Backpack
            cash.Value = cash.Value - 5 -- subtract the amount of cash you need to purchase
        end
    end
end)

Finally, delete the LocalScript inside the TextLabel and replace it with a script. Not much difference, but here is the script if you need it:

while true do
    wait() -- prevents crashes
    local cash = script.Parent.cashv
    local cashDisp = script.Parent
    cashDisp.Text = "$"..cash.Value -- sets it
end

That's all, I'd appreciate it if you accepted the answer. Any issues, feel free to ask! :)

I believe the problem lies in the Value script. You would need to put it in a loop; that way, instead of updating the display just once, it will constantly update it. Here is the complete code:

local cashdisplay = script.Parent
local cashvalue = script.Parent.cashv.Value

while true do
    cashdisplay.Text = "$"..cashvalue
    wait()
end