There's an issue with the buy system where players can still purchase items without being near the buystation after using it. This allows people to abuse items like disposable RPGs, farming money and clearing everything in their path. While it's fun at first, it can ruin the experience by enabling players to speedrun the maps.
Also there's an issue in cf_coopleve08 where players can exploit the portal message by staying inside it. This continuously triggers the message, "This portal needs a keycard," every 0.1 or 0.01 seconds for all players. This can be fixed by editing the trigger brush flags and ticking the Fire on Enter spawnflag. Doing so will ensure the message plays only once when the player enters the brush.
Edit: I've seen you've used the trigger_changelevel to trigger the message on item fail, you can replace the fail target of the brush to a trigger relay so it will trigger the message then wait for a second before triggering again.
