Very interesting post from the Baymard Institute (e-commerce usability experts) regarding how first-time users were observed to rely heavily on the main navigation options and the homepage content to determine the type of site they’d landed on.
Here's a few snippets:
"25% of the test subjects consistently scrolled far down the homepage and then back up again in order to quickly establish an impression of the site’s product range. Alas, this lead to many misconceptions as numerous of the tested sites displayed a very narrow selection of their product catalog on the homepage."
"Most of the sites where first-time users were correctly able to infer the type of site, visually featured at least 30-40% of their main product categories on the homepage (i.e. the first level of product categories)."
"The litmus test is easy: does a quick glance over your homepage adequately convey your store’s product diversity? If not, first-time visitors may be drawing false conclusions about the scope of your site’s product catalog."