How to make a child entity automaticially reference back to parent entity when created using inline entity form?
This has been acheived using Rules:

Export of Rule:

{
        "rules_ifs_backlink_populator" : {
        "LABEL" : "IFS backlink populator",
        "PLUGIN" : "reaction rule",
        "ACTIVE" : false,
        "REQUIRES" : [ "rules" ],
        "ON" : [ "node_insert", "node_update" ],
        "IF" : [
          { "node_is_of_type" : {
              "node" : [ "node" ],
              "type" : { "value" : {
                  "auction" : "auction",
                  "estate_sale" : "estate_sale",
                  "garage_sale" : "garage_sale"
                }
              }
            }
          }
        ],
        "DO" : [
          { "LOOP" : {
              "USING" : { "list" : [ "node:field-ifs-add" ] },
              "ITEM" : { "list_item" : "Current list item" },
              "DO" : [
                { "component_rules_create_entity_reference_back_link_" : { "child_param" : [ "list-item" ], "parent_param" : [ "node" ] } }
              ]
            }
          }
        ]
      }
    }


Export of Component:

{ "rules_create_entity_reference_back_link_" : {
    "LABEL" : "create entity reference back link ",
    "PLUGIN" : "rule",
    "REQUIRES" : [ "rules" ],
    "USES VARIABLES" : {
      "child_param" : { "label" : "Child Parameter", "type" : "node" },
      "parent_param" : { "label" : "Parent Parameter", "type" : "node" }
    },
    "IF" : [
      { "AND" : [
          { "node_is_of_type" : { "node" : [ "child-param" ], "type" : { "value" : { "ifs" : "ifs" } } } },
          { "entity_has_field" : { "entity" : [ "child-param" ], "field" : "field_auction_ref" } },
          { "data_is_empty" : { "data" : [ "child-param:field-auction-ref" ] } }
        ]
      }
    ],
    "DO" : [
      { "data_set" : {
          "data" : [ "child-param:field-auction-ref" ],
          "value" : [ "parent-param" ]
        }
      }
    ]
  }
}