The most common and most likely answer to this crossword clue is the 8 letter word PROCURER
I've seen this crossword clue in The Guardian
P
R
O
C
U
R
E
R
More clues leading to the result PROCURER
Buddy explains!

The straight part
We know that "He obtains favours" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case he obtains favours = procurer.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.
What does PROCURER mean?
PROCURER noun- A person who procures or obtains things, especially one who procures customers for prostitutes.