What are the visa overstay penalties for Thailand?
Can you provide official links?
At the bottom of Thailand Visa Advice (Part 4) it says:
You must pay a fine of 500/day, but not exceeding 20,000 baht before you are allowed to leave the Kingdom of Thailand.
Interestingly, the 20,000B maximum is is 40 days @ 500B/day. There is no quantitative difference until you hit 90 days (Part 3.1):
An alien who overstays more than 90 days beyond his/her permitted date will be banned from re-entering the country for 1 year, starting from the departure date.
Further penalties are listed for overstays beyond 1 year.
Many people routinely overstay one or two days, but the ugly stamps may well affect the decision of an official to let you into the country later on, especially in cases where the decision is up to the discretion of the officer (eg, you've got a lot of visa-free entry stamps).