...and why this is an excellent idea, especially for first-time visitors.
I was walking my dog this morning, and a couple was arguing with their taxi driver (who didn't speak much English), complaining that he had taken them to the wrong address. He hadn't, though - they had just not checked out the building their rental apartment is located in, and couldn't believe their eyes (or their luck).
They assumed that they would be staying in one of the charming ancient buildings that can be seen from the nearby public garden - instead, they rented a place in an ugly modern building (that was built in the 1980's by an insurance company), that happened to be within shouting distance of the flowerbeds (many photos of which were featured in the apartment listing).
Since my dog was busy checking out the thousands of cigarette butts on the sidewalk, I had lots of time to talk with this couple. First time to Paris, first time renting an apartment, first big let-down - and I got the feeling this wouldn't be the last problem they would face during their stay, since they were asking a stranger on the sidewalk a whole bunch of questions they should have found out about before they even bought their plane tickets.
Even if you've been to Paris several times before, things do change, and it's a good idea to find out about both the building and the neighborhood you will be staying in, before you commit to a hotel or apartment. Get the exact address, if possible - or at the very least, the nearest intersection - then take the little YellowMan on a walk and Zoom In and Out to see what's what. GoogleWalk and GoogleMaps are easy-peasy to use - the Street View is a real revelation. Check the date at the bottom of the photos - it's usually a year or two old, but better than nothing.
And one more word of advice - if an apartment or hotel features lots of photos of monuments, gardens, etc, and very few of the interior and exterior of the actual place you will be sleeping in, you should either ask for better photos or look for another place to stay. Don't end up like those people I met this morning...