1e480021_iness___Local_Search___Part_15__Additional_details
[Date/Area Affected / Issue] 12/15/11 Places: Owner can not respond to reviews if the listing is claimed into two accounts [Reference URL] Places Forum Post [Additional details] 
report in the German help forum as in URL-column – as well as in the English Forum: here. This is an old problem that showed up first in 9/10 here. According to Google it is because there are two account holders and the one trying to answer is not the dominant one. However, given that the problem seems to pop up periodically in clusters it is possible that somehow the secondary account is automatically given prominence.
Google Places (Maps & Local) | Understanding Google My Business & Local Search - Part 15
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