The most common and most likely answer to this crossword clue is the 4 plus 3 plus 9 letter word MOVE THE GOALPOSTS
I've seen this crossword clue in The Times
M
O
V
E
T
H
E
G
O
A
L
P
O
S
T
S
Buddy explains!
The straight part
We know that "Unfairly achieve desired results" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unfairly achieve desired results = move the goalposts.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.