Web developer hosting on his own subdomain as well as the live site

Hi BHW,

I'm really angry about finding out a potential clients website has been developed on a live site for over 8 months on the designers subdomain as well as the clients own domain, meaning duplication but worse, every page of the designers subdomain is indexed and ranking in Google!

I'm seeing them today to discuss the issue and just wanted to check with you guys what I might say as a solution, i'm guessing disavow and getting him to pull it down. The thing is, its an interview so I want to be prepared for any question.

Thanks in advance!

I don't think that you can do much about it, if designer doesn't want to cooperate.

Otherwise, you can ask the designer to create robots.txt file for the root of the sub-domain, something like this:
or

Beside this, you can also force Google to remove pages in question from index, by submitting form on the https://www.google.com/webmasters/tools/removals (you would need to first verify domain/sub-domain in your Google account).

And on top of that you should make redirects from designer sub-domain to main domain via .htaccess, like so:
this will redirect index file, and if you want to redirect specific pages, then you can use:

When all of this is done, you can make sitemap file (or create it automatically on https://www.xml-sitemaps.com/) and submit it to search engines (for Google you can use their Google Search Console).

Excellent contribution, thank you so much!!! I hope I can win that client now, really appreciate it!