There have been some reports of bearing troubles... but honestly that coulda been neglect as easily as any thing else.
The BIG problem, where the danger is in making a wallyworld bike into a motorized bicycle is in the really
cheesy rims. The frame welds tend to be fine as metalliatic mentioned, tires can ofc be upgraded and the shifters and whatnot don't really matter even if it's got 'em. I've got a walmart MB, I'd not even consider letting someone ride it w/o warning them about the rims. The bearings have gotten a lil runout despite maintenance, but it's also got a lot
of miles on it now lol
It's those bdanged junk marshmallow rims - compounded by the obvious truth that anyone willing to only spend $80 on a bike isn't about to have them trued, let alone replace them with quality. Add in the kit "rag joint" sprocket mount... erg...
I only mention this because of the potential danger, I do actually recommend that people not rush out to buy the best bike they can find for their first motorized bicycle - it's a learning process and the first is best viewed as a test platform. Yet I'd still not be comfortable selling
such to others, without the build process to learn from and ignorant of the weaknesses of a motorized bike... well... it might
work out ok but I have my doubts.
If I were inclined to sell bikes, I'd be forced to hike the price a lil and get some double walls laced on there jus' so I could sleep easy