If they can be nailed wrong, they will be.
It seems that more than half of the decks we inspect have a problem with the joist hangers. For some reason (and its probably price) people want to buy a smaller joist hanger than necessary saving a few dollars and putting the deck in jeopardy.
Joist hangers must match the size of the joist it is supporting, so a 2×8″ joist needs a larger joist hanger than a 2×6″ joist.
The joist hanger to meet the manufacturers load bearing capability must be attached using specially approved nails or screws, which means that finish nails, drywall screws, framing nails and least of all and most often used “roofing nails” and not approved. Roofing nails will fail because if they are put under a load the heads will break off.
Then there must be a nail in every nail hole to meet the manufacturers requirements.
Joist hangers may not be bent, cut or otherwise modified to form a different shape.
Joist hangers have a finite life expectancy, the galvanized (shiny) will wear off and they will start to rust and deteriorate. At that stage they are considered to at the end of their functional life and need to be replaced.