There is such a thing as a re-tread. If a tyre has enough rubber left on the original carcass, the existing tread is shaved off and a new strip of rubber is vulcanised over the top and the tread is cut into the new rubber. Re-treads are relatively safe, although not as good as a new tyre, but they're infinitely safer than carving chunks out of a worn tyre by hand and passing that off as a new tyre. The tread wear bars are there for a reason. Cutting them off and digging the rubber out even closer to the carcass is NOT how you make a re-tread. If you see something that looks even half as sketchy as the "tread" in this finished product, just walk away:
