2022
When you come across two (or sometimes even more, but for the sake of simplicity I will refer to 2 in the rest of this post) mentions of the same point of interest (POI), you should report one of them as duplicate. You do this by going to Suggest an edit, click Remove this place and then select Duplicate of another place from the drop-down menu containing the possible reasons for removal. (Don't worry about the Add a photo-option on that page, as that is not relevant in reporting duplicates - it can be useful for some of the other options in the list, like Not open yet or Private place or home). Usually, you will then be presented with another pop up screen that lists one or a few other POIs which Google suspects could be the 'correct' one, asking you to indicate which of those you consider to be the correct one. At the bottom of that list there is also the option to indicate None of the above in case the one you meant is not listed. So far, so good: the process is pretty straightforward. But what can be much trickier to do, is to decide which of the two is the one you want to report as duplicate, and which is the one that should stay on the map.
In some cases this is quite easy to decide: one of them has no reviews, no photos, and the pin is located 50 meters away from the actual location, while the other has 12 reviews, 6 photos and is located correctly. But in other cases, both POIs might have dozens of reviews and photos, so which one should you pick then?
Fortunately, there is quite good news at this point: it doesn't really matter. Unlike most of the edits that local guides suggest, the process to deal with reported duplicates always involves human intervention. Someone at Google will have a look at the duplicate you reported (at some point - it can take a while: for duplicates I have personally reported, I have seen response times ranging from 1 to 139 days), and instead of simply keeping one of them and deleting the other, the 2 POIs are merged to make sure all relevant information is preserved. So the one that eventually remains, will e.g. 'inherit' the reviews the other one had.
Keeping this in mind, the best practice for duplicate POIs is to make sure that the person who will eventually have a look at the reported duplicate has an easy job when looking at the 2 POIs. So, for both of them: check that the name is correct (and adapt if needed), move incorrect pins to the correct location, make sure both have the most appropriate category, etc. It is important to make those changes before reporting the duplicate, as that will obviously increase the chance that the algorithms detect the duplicates when presenting you the pop up screen I mentioned earlier. And of course correct information on both POIs is also very helpful to the Google team processing duplicates.
One more thing: to see if and when your duplicate reporting was processed, it's no use checking the Edits section of your contributions, as you only receive a notification by email for duplicates.
Other posts in this series:
Best Practice: Find new places to add to the map
Best Practice: Fix inconsistencies in chains
Best Practice: Learn to be patient
Best Practice: Find the right category
Best Practice: Industrial Zones
This is a revised version of a post that I had published earlier, before the switch of the forum to its current format.
Disclaimer: the practices described here as best practice are my personal interpretation, and I don't claim any level of official endorsement.
