What about companies that put their own details down as the registrant? Does that mean google thinks all of those sites are owned and controlled by one person. That would be a big mistake because of course the domain registration company has no control at all.
Google (so they say) always strive for accuracy so one would assume that they dont make that link or at some point will correct it if they do currently.
Infact with some very large registration companies/ISPs putting their details in as the owner its hard to imagine top google brains sat round a desk and decided to link all sites with the same name. Its easy to see why that would go wrong!
I have domains registered in both ways but actually prefer the above because I dont want my own name on the contact details should any stalker want to try and track me down

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The other thing that was discussed recently on the official google blogs was using subdomains. Google said that these are treated as individual domains and if one ranks well it well hold no juice over the other subdomains. A while ago I bought a particularly snappy domain that I can now use to create infinite subdomains , eg pillows.shop.com or elephants.shop.com you know what I mean. Seemed to have no problem ranking well, you build a brand, and save money and time managing domains!
Of course everyone has a different opinion/experience as to what works best - so let us know how it goes

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