If your scope is clear to start with and gets blurry as the barrel warms from shooting or as the day heats up, there is nothing wrong with the scope. I have a nice Leupold that does the same. It is just magnifying heat waves, known as mirage when out in the field between you and the target, barrel mirage when it is hot air rising off the barrel.
If you have barrel mirage an inexpensive approach is the Sinclair Shade which looks like a section of Venetian Blind attached to the barrel with Velcro. Only $4
http://www.sinclairintl.com/cgi-bin/...-7X&type=store
I have seen barrel length sunshades screwed into the scope but they are more expensive and I could not find a source on a quick Google.
If you have real mirage out over the range, the only thing to do is to turn down the magnification til it is not a bother to you. You can learn to read the mirage and estimate wind effects at long range.