Can't speak for JMD specifically, but have not had much issue with any US brokerages. They are a bit more worried about getting sued, plus I believe you can threaten to pursue payment through their insurance company and they get real eager to get you paid if you do that.
That being said, any major payment delays generally seem to be software based as the check printing programs can't seem to recognize Canada, or postal codes.
Just my $0.02
Thanks for replies. We did not connect on this shipment. They did not know what customs docs or custom brokers are for, for cross border shipment and trying to find where they can get it.