Looks like they sold you the 4.5in mini Silent Spinner. Pet stores don't have good knowledge for the most part about hamster needs.
A 6.5 in Silent Spinner would have been the better choice. Your hammie would be much happier in a bigger wheel. He'd have more room and wouldn't feel cramped.
I think the 9 in yellow Silent Runner is awesome for dwarves. Alos, the 8in Wodent Wheetl is real nice compared to the Silent Spinners which aren't being made very well, although it seems that they are trying to correct this problem from the wheels I've seen in Pet-Co & Pet Smart lately.
You want a Silent Spinner that doesn't have any resistment to it. If you spin it 3-4 times and it stops spinning then the dwarves can't move them and that wheel is defective.
Edit: I didn't read through this whole thread, don't mean to contradict anyone