Is there any way to hook into an event for an item purchase?

I'm trying to make a vendor where some items can only be purchased if certain conditions are met. There doesn't seem to be an 'item purchased' hook anywhere, but I'm wondering if anyone has done this in a more hacky way?

Ideally, I'd like to be able to do this:

function itemPurchased(event, player, item)
   local arbitraryCondition = GetPointsFor(player)
   local itemID = item:GetEntry()
   if(itemID == VENDOR_ITEM_1) then
         if(arbitraryCondition >= 3000)then
               return true;
         else
                 player:SendBroadcastMessage("Requires 3000 arbitrary condition points dumbass")
                  return false; (or, like, player:RemoveItem(itemID, 1))
         end
   end
end



Obviously, I'm using LUA. If anyone has any insight on this it would be greatly appreciated. Thanks guys.