Keeping 3k baht is reasonable.
The landlord may have cancelled with other prospective tenants during the 3 hours. Also, changing your mind wasted the landlords time.
If you ever feel pressured again or uncomfortable, just ask to use the restroom, then leave out the door when they are in the other room. If the door is locked you got bigger problems!
Another side note. Anytime anything is rushed it’s a big red flag. You need to ask yourself why they are desperate. Usually they are trying to hide something and want to close the deal before you see some kind of problem. Includes landlords who get irritated when you take the time to inspect a property. The typical excuse is you are wasting their time.
I used to buy used cars and certain sellers don’t want to allow mechanical inspections or let you “kick the tires” because they are “too busy”. Same principal, they are hiding something.