Bests & Worsts Reviews from Amazon

I have other Littmann stethoscopes that are great. I decided to take a chance and get one off of Amazon, however I wonder if this one is a knock off. Side by side comparison of other Littmann Classic III stethoscopes show that this particular one has very limited auscultation abilities. It is worse than the back up stethoscope I bought for $25, in that I cannot actually hear the heart very well at all, much less pick up a low grade murmur or abnormal lung sounds. I missed the return window because I work all the time and I didn't have a day to take the package to the post office. I would be very cautious in this purchase. It does not cost anything additional to get a stethoscope from a store where you can try the product first and know you are getting a quality product. I have not had this issue with any other stethoscopes of this brand, and that's why I wonder if this is one is a total knock off.