The most common and most likely answer to this crossword clue is the 4 letter word SOLD
I've seen this crossword clue in The Guardian
S
O
L
D
More clues leading to the result SOLD
Buddy explains!

The straight part
We know that "betrayed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case betrayed = sold.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 SOLD mean?
SOLD verb- (ditransitive) To transfer goods or provide services in exchange for money.
- To be sold.
- To promote a product or service.
- To promote a particular viewpoint.
- To betray for money.
- To trick, cheat, or manipulate someone.
- To pretend that an opponent's blows or maneuvers are causing legitimate injury; to act.
- Salary; military pay