The most common and most likely answer to this crossword clue is the 1 plus 3 plus 2 plus 1 plus 4 letter word A PIG IN A POKE
I've seen this crossword clue in Financial Times
A
P
I
G
I
N
A
P
O
K
E
More clues leading to the result A PIG IN A POKE
Buddy explains!

The straight part
We know that "a risky buy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a risky buy = a pig in a poke.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.