The most common and most likely answer to this crossword clue is the 7 plus 5 letter word CONTROL FREAK
I've seen this crossword clue in Financial Times
C
O
N
T
R
O
L
F
R
E
A
K
Buddy explains!
The straight part
We know that "one like Svengali?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one like svengali? = control freak.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.