You mean the yearly extension that you need to report every 90 days. But you can report online, it take 5 min, no need to drive anywhere except on your first report (any 2nd, 3nd, etc, can do online).
I'm currently on 90 days single entry Non O and can extend 60 days once. Before, I was on visa exempt and extended once for 30 days and a 2nd time for 60 days. The reason why you can do both on visa exempt or tourist visa is that you first extend for tourism reason but than extend again for a different reason (marriage). But when you enter on Non O you are already on a marriage visa so can only extend for that specific reason.
Do not read your DM, your friend does not need an agent. Your friend can enter Laos today and get 30 days visa exempt. Mukdahan border is hassle free border, they do not ask for anything nor question you. Your friend should have done that right away since he's only gonna be in Thailand for 7-10 days. p.s: As said above, Savannakhet has had a 2 consecutive tourist visa rules for a long time. And also if you have history of volunteer visa you cannot get tourist visa there anymore.
Then why is he doing a tourist visa if he's only going to be in Thailand for 7-10 days? He should have in and out Laos in 30 min hassle free. He can still leave Laos today hassle free and get 30 days.
p.s: Savannakhet only issue 2 consecutives tourist visa, not 3 or more, thats why he got denied. p.s.2: Mukdahan is hassle free border. Wont be ask anything.