General Warning: Solications that look like Bills
This is just a general warning that it is common practice for some disreputable companies to either mail or e-mail you solicitations that look a lot like official invoices/requests for information.
In the case of the advertisements disguised as bills, if you read the fine print (usually in microscopic type on the back), you discover it is for useless search engine placement, advertising or a permission form to give their company the ability to transfer your domain to their services and usually at a much higher yearly renewal rate.
Any customers who feel uncertain about whether a particular billing is legitimate, please feel free to contact me by e-mail, phone or fax and I will be happy to look it over and let you know if it is a scam or a legitimate billing.
Some web resources on the subject:
About.com - Ads That Look Like Bills
Phishing - Wikipedia.org