Let me explain in bullet form what I'm trying to achieve.
1. A user visits a single ad for example see: http://inthebunch.co.za/classifieds123/listing/off-road-2010/
2. The user then wants to see all the ads by that specific advertiser.
3. The user clicks on a link that takes them to that specific advertisers' author/archive page
4. On that page there is grid display of the advertisers' ads
Solution:
1) The user clicks on a link that takes them to that specific advertisers' author/archive page
You can setup the link to post author archive page with Views shortcode: [wpv-post-author format="link"]
For example, edit the layout "Single - Ad", the visual editor cell "Advertiser", add a line:
[wpv-post-author format="link"]
More help: https://toolset.com/documentation/user-guides/views-shortcodes/#wpv-post-author
2) On that page there is grid display of the advertisers' ads
Createa Views wordpress archive for author archive page: