Have to agree with Jim, Think your bike shop guy is mistaken. literally have only used one good wheel for a build. The rest have been Walmart or some other lesser brand bikes with cheap and cheesy wheels and spokes and have yet to break one spoke. As the broken spoke thing comes up a lot, I always wondered how come my cheapie builds never break 'em. I really dunno but think the most plausible answer is in not over tightening.
I am more pondering then suggesting.
Building the Honda, I read Bicycle Engines, Motorized Bicycles, Bicycle Motors, Motored Bikes: 2-Stroke & 4-Stroke Kits!
installation page. (was very good) But on the sprocket, is states that when getting the wobble out, tighten it down then loosen, not tighten to get it even. Obviously, not to lose or slappen' around freely.
I am really not suggesting any thing and am just wondering. Helped a buddy build a bike yesterday. Always makes ya worry.