​Leaning retainer walls are an expensive repair, and very dangerous for your family, costing anywhere from $450 to $600 per m² for a concrete block replacement type. This wall is leaning over 220mm and because any wall built higher than 1 metre requires engineering. The repair, to be legal and complying with the council will require certification prior to construction. When looking at a wall such as this one the total overall repair could be over $12,000 just for the rear retainer wall. Unfortunately the properties side retainer walls were also failing in a similar way and also requiring replacement.

​Deck safety is an often overlooked issue with a house. This example has no bolts connecting the non structurally graded timber posts to the bearers (Painted to look like steel posts).
Round CCA logs are often untreated all the way to the middle, allowing for termite entry and the cut end must face upward as only the original post ends have full treatment.  As this deck was in a coastal environment, it is subject to high corrosion, so the nails used are not adequate in holding the bearers in position. The posts should be seated into a cut out section to stop the possibility of the pine bearer twisting and bolted with minimum of 2 galv M10 Bolts. The base of the post ideally should be bolted into galv post shoes, to reduce the termite risk. 
Overloading a deck is a common area of concern with items such as BBQ's, Furniture, air conditioner compressors and large potted plants contributing to a possible deck collapse. If the area was not designed to take additional loads where you have added them, its probably not safe to do so.