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Thank you for the very clear response!

The sandbox is on a subdomain of the developer's website. ourSite.theirDevSite.com/sandbox/

Their robots.txt actually redirects to their main website (why? no idea).

But the developer should verify the subdomain sandbox site in GWT/BWT, then disallow everything with robots.txt (and stop redirecting it), then request the entire site to be removed. Anything I'm missing?

An ecommerce I'm helping is getting a complete redesign.

Their developer had a sandbox version of their new site for design & testing. Several thousand products were loaded into the sandbox site.

Then Google/Bing crawled and indexed the site (because developer didn't have a robots.txt), picking up and caching about 7,200 pages. There were even 2-3 orders placed on the sandbox site, so people were finding it.

So what happens now?
When the sandbox site is transferred to the final version on the proper domain, is there a duplicate content issue?
How can the developer fix this?