The most common and most likely answer to this crossword clue is the 6 letter word HIRING
I've seen this crossword clue in The Daily Telegraph
H
I
R
I
N
G
More clues leading to the result HIRING
Buddy explains!

The straight part
We know that "Letting" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case letting = hiring.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 HIRING mean?
HIRING verb- To obtain the services of in return for fixed payment.
- To employ; to obtain the services of (a person) in exchange for remuneration; to give someone a job.
- To exchange the services of for remuneration.
- To accomplish by paying for services.
- To accept employment.
- The act by which an employee is hired.
- A fair or market where servants were engaged.