I think that logic's faulty, too, Dean. The interim provider certainly has right of control over it's own equipment; if the provider feels that spam and such are impeding it's ability to provide such service, it is certainly within it's rights to fix the problem. If it's customers don't like this, it's certainly not impossible for it to move to another provider.
I would have to agree with this, but I would say that the caveat is that the ISP should notify the customer (somewhere, anywhere) that they use the RBL (or at least that the ISP reserves the right to block domains and/or hosts from connecting/sending to the mail server). It can be in the fine print of the multi-page AUP that the customer gets shoved under their nose, but it should be in there. Derek