The rules are simple: 1. C. Botulinin is everywhere. It is in the food you are preserving. Deal with it. 2. Heat kills C. Botulinin. Propper pressure canning times and temperatures of properly diced foods will kill it. 3. Acidity inhibits C. Botulinun metabolism. Boiling water bath canning of high acid foods like dill pickles is sufficient to keep any remaining microbes from producing toxins. (Botulism toxin is a metabolism byproduct. ) 4. 10 minutes at boiling temperatures before serving will break down botulism toxin. 5. When in doubt, throw it out.
Was that hard?
The most subtle mistake to make is if the canning recipe says dice into 1/4 inch cubes, don't use a different size. It changes the convection currents in the jar and it may not reach required temperature/times in the core. Also be careful with home made salsa as the acidity can vary wildly depending on numerous factors.