[jacquesm]

Good point. It requires disassembly, and if you're not comfortable with that it is a lot harder to get a good idea on this. But there are plenty of videos and photos online of various disassembled packs from high volume manufacturers.

Quality cells are a relatively small group of brands so that should be easy enough to check for, and you'll know looking at just one side of a cell group whether or not it was put together half decently or whether it is messy.

Stuff to look for: loose balance wires, bad welds (welds that don't penetrate so they're loose), pointy edges of connecting strips that touch the plastic insulation of the cells, insufficient spacing between the cells, insufficient insulation near the welds.

For one-off purchases this won't help, but if you are a reseller or larger purchaser then it definitely is a good idea to tear down a pack and inspect.