Please cite your reference.  Financial providers are required to under
APRA guidelines, but I believed the 'jury was still out' regarding
websites as "official documents".

But as you are demonstrably incapable of doing so yourself, I have taken
the time to find the information on their website, and will now detail
the procedure so you can follow it at your leisure.

Step 1. Open 'www.ebay.com.au' in your preferred web browser.
Step 2. Scroll to the bottom of the page, and click on "About eBay"
Step 3. Look for the box that says "Contact Information".  In that box,
it says "Find out where our offices are located." The words "our
offices" are hyperlinks.
Step 4. Click on "our offices" (see Step 3 to locate them) and there are
their contact details.

[sigh]

I do this only because the dogs are outside peeing and I have a moment
to spare before putting them, and then myself, to bed.

You may like to check with ASIC.  I did, and they don't mention websites
as a requirement for publishing an ACN/ABN.

Now I'm not a lawyer (if I was I'd charge you for the advice tonight),
but you can argue about websites all you like.  I've yet to see anything
that compels the publication of ACN/ABN on them, other than for
invoices/receipts/shopping cart style pages.

Anyway, fill ya boots.
taken from:
<http://www.asic.gov.au/asic/asic_pub.nsf/byheadline/Australian+Company+Numbers?o
pendocument>

A company's ACN should appear on all of its 'public documents' and
'eligible negotiable instruments' [s.153]. The items on which it should
appear include:

   * all documents required to be lodged with ASIC;
   * statements of account, including invoices;
   * receipts (which are not machine-produced);
   * orders for goods and services;
   * business letterheads;
   * official company notices;
   * cheques, promissory notes and bills of exchange; and
   * written advertisements making a specific offer which is capable of
being accepted (such as by the completion of an order form).

If a company's name appears on two or more pages of a document or
instrument, the ACN must be shown on the first of those pages following
the company's name.

Where a number of separate companies are listed on a document (eg, a
letterhead) the ACN of each should appear and in such a way that makes
clear the company to which each ACN relates.

While there are no specific requirements as to how an ACN should appear
on a document, it should be clear, easily readable, and obvious as to
the company to which it relates.

The ACN should be identified by the words 'Australian Company Number',
or by the abbreviations 'ACN' or 'A.C.N.'.

Australian Business Number
If your company has an Australian Business Number (ABN), you may use the
ABN with your company's name in place of the ACN on company documents
and negotiable instruments, provided that:

   * your ABN includes your nine digit ACN; and
   * the quotation of the ABN is effected in the same manner in which
quotation of the ACN would normally occur. (For example, a company is
required to place its ACN with its name on the first page where that
name appears in a document).

For further information about the legal requirements in relation to
Australian Business Numbers, contact the Australian Taxation Office.

No doubt at all those of the aluminum skull cap brigade will always do
business with him. You are known not only by your actions but by the
company you keep. Did you know that?

At least for the time being, I get to say who I'll trust a description
from and decide what the value of (if any) warranty I'm likely to get
might be before I commit hundreds of dollars to that trust ...From here
it's zero on all fronts for you and him.