Water in the trunk, is this really prevalent issue with older Toyota Corrolla's?

I am in the market for a new/used car and am considering buying either a 2007 or 2009 Toyota Corolla. The two I have found are in great shape despite their miles and age. The 2009 model has 171 k on it, but it is one owner and very well maintained. The guy at the car lot said he has found that some of the Corollas tend to leak water into the trunk wheel well. I was just wondering if this is wholly prevalent? Is it certain years more than others? Should I worry myself to death over something like this? Is this something my auto mechanic can detect for me? I did detect a bit of a smell going in, but the car had also been recently detailed, so it could very well be the carpet shampoo.

Second, the 2007 model has 141,OOO miles to the 2009's 171, 0000 miles.. Do miles matter so much compared to how well a car has been cared for? The 2007 model has had had three owners to the 2009's one. I do need this car to last me a while, but I am also on a budget, unfortunately.