Fastener quality can be all over the place. To the point that if you buy a batch at the local building store that you can get excellent quality or stuff that isn't usable at all. It can be pretty tricky to determine what you've got without opening the box, but looking carefully at the finish of the threads on bolts and screws will tell you about the quality. As will length variation, the presence of blinds (screws that have no thread), heads that look sloppy or that have varying distance to the start of the thread and so on.
A typical screw or bolt needs three to five threads to reach maximum strength, if you just screw a screw into a plate or sheet of wood for three to five threads you should be able to torque it down to under it's sheer strength (which for almost all fastener dimensions and materials is specified). If it breaks then you can consider the whole batch faulty.
The easiest way to ensure that you get good quality is to go for the premium brands of fasteners, it won't be cheap but at least your stuff won't fall apart when you need it most. Avoid retail outlets, buy where the professionals buy.
A typical screw or bolt needs three to five threads to reach maximum strength, if you just screw a screw into a plate or sheet of wood for three to five threads you should be able to torque it down to under it's sheer strength (which for almost all fastener dimensions and materials is specified). If it breaks then you can consider the whole batch faulty.
The easiest way to ensure that you get good quality is to go for the premium brands of fasteners, it won't be cheap but at least your stuff won't fall apart when you need it most. Avoid retail outlets, buy where the professionals buy.