The most common and most likely answer to this crossword clue is the 8 letter word LEVERAGE
I've seen this crossword clue in The Daily Telegraph
L
E
V
E
R
A
G
E
More clues leading to the result LEVERAGE
- Purchase made by the 4 dn, always with silver inside
- Purchase drink, having left for Belgian capital
- Strategic advantage gained by tipsy lager drinking first lady
- Girl’s last, always taking time to make purchase
- Influence American to abandon holiday passion
- Pull handle on time
- Dame Edna supports learner making purchase
- Enhanced power of guy in bank
- Influence of European currency leading to English anger
- Party reversed decline in influence
Buddy explains!

The straight part
We know that "purchase" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case purchase = leverage.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 LEVERAGE mean?
LEVERAGE noun- A force compounded by means of a lever rotating around a pivot; see torque.
- By extension, any influence which is compounded or used to gain an advantage.
- The use of borrowed funds with a contractually determined return to increase the ability of a business to invest and earn an expected higher return, but usually at high risk.
- The ability to earn very high returns when operating at high capacity utilization of a facility.
- To use; to exploit; to manipulate in order to take full advantage (of something).