What are the penalties and implications for overstaying a visa in Thailand while on amnesty?

Hello, I am asking for a friend.

He has a EU passport, a valid work permit and an expired business visa.

He is on amnesty now and waiting for his business visa for the next destination (Vietnam) which may or may not come before the amnesty expires.

He is considering overstaying for up to a week, here are the questions that he asked me to put forward:

- Is the penalty 500/baht per day and nothing else?

- Overstay up to 7 days means blacklist?

- Does he have valid alternatives (going back to Europe isn't a viable option)?

Thanks.