Sounds like he needs to get himself an SPF DNS record (assuming his email is at the linked domain).

Yes, his situation sucks, and it's also bad that seemingly no-one at Google cares (though as was mentioned in the comments there, they do have phone + email support for paying apps customers). It doesn't really sound like Google's fault or problem, because raising whatever limit they have on his account won't fix a problem with someone presumably using his misconfigured domain to send spam, triggering the limit in the first place.

Of course, that doesn't change the fact that Google really doesn't seem to value customer service.