The most common and most likely answer to this crossword clue is the 11 letter word COMPLIMENTS
I've seen this crossword clue in The Sunday Telegraph
C
O
M
P
L
I
M
E
N
T
S
More clues leading to the result COMPLIMENTS
Buddy explains!

The straight part
We know that "Seasonal good wishes" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case seasonal good wishes = compliments.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 COMPLIMENTS mean?
COMPLIMENTS noun- An expression of praise, congratulation, or respect.
- Complimentary language; courtesy, flattery.