The visa is legitimate, but it is not ideal for everyone. If you are working here legally then it is a complete waste of time since you still need to obtain a Non-immigrant B visa and Work Permit.
It looks as though the first stamp wasn't clear enough so they voided it, "without prejudice" which simply means the cancellation has no prejudicial effect on your visa status. Then they stamped a clearer one in the passport/ Just count yourself lucky they found the inkpad for the second attempt.
is absolutely correct, although I would add that the manner in which the laws are applied does change. We really do have the work permit and visa process organized now but every year we are asked for something new, presumably because someone wants to prove how important or clever they are.
Thanks. I completely forgot a few years ago and wandered into Immigration several weeks overdue and just paid ThB 2,000, so it seems nothing has changed.