i agree with other friends here , you were upset for rite reasons , if you can hire others , do so , even if they fix cosmetic issues , i feel it can have design faults as well i will list few things i see
The type of rock , i have doubts , im not around your place to say accurately how they do in your environment but seems to be yellow clay rocks to me and if they are wet they will dissolve slowly , try to touch them if they feel like fragile & orange dust cumming out and not smooth solid feel .
in some places gravel is very thin that if any one walks on it or with time it will fall away , it will harm the liner and expose it , will look bad too
there are a lot of wrinkles all around , if water clears it will look worst
border lacks rocks , theres only one row of rocks thats not enough to hide liner , in some places shallow 1feet shelves are empty beside rocks that needs to be completely filled with gravel or plants or rocks to hide liner , to give natural look . if you dont have enough to hide it then it should not be left shallow , should be steeper to hide it
The gravel has no guideline/control, it will drop down inthe pond gradually from all sides , there seem to be no support or restriction , how will you clean
1st thing it needs is full cleaning again because all the rocks , gravel had this sand in it , its too much for a new pond , if it was old pond this would be managed by echo system and settled quick , but theres no algae or bacteria or plants , rocks to take care . i think waterfall is circulating the sand or its rain bringing it , if you have alot of rain the create borders to block easy flow in pond .