Since someone else installed the coaster brake assembly both times, there is no way for you to verify that it was done correctly. I have got to be very honest, after 4 years of building and riding my own bikes, I trust my own mechanical abilities more than that of a bike shop. I have literally built my current bike piece by piece, and when I put something together, I know whether it was done right or not. Just because it was done at a bike shop does not mean it was done correctly. And the walmart employee? I'm not even going to touch that. I will agree that a coaster brake should not be the only brake on a motorbike. I personally run a front drum and love it. I don't typically use the coaster brake much at all. But a bent axle is almost certainly due to improper hub assembly. And like I said, there is no way to verify if the assembly was correct one way or the other, since you didnt do it yourself. And since the replacement axle was almost certainly not a huffy axle. Two different brands of axle with the same failure, its almost certainly got to be improper assembly or improper operation. Coaster brakes may not be the best choice of brake for a motorbike, but there are quite a few people using them and not bending their axles. So I for one am still not accepting that the parts themselves are to blame.