Whether it is your deck , a friends, or a place of business you are supporting, do a quick look at it to trust you are safe.
What to look for: Properly supported surface, rails, and stairs, and overall support by posts or the ledger board. Do you feel it move as you walk on it? Kindly recommend an inspection from a Certified Home Inspector such as myself. Let's inspect it together for your safety and others.
Here are some graphics to help you, (thank you , INterNACHI).