The most common and most likely answer to this crossword clue is the 10 letter word SNEEZEWORT
S
N
E
E
Z
E
W
O
R
T
More clues leading to the result SNEEZEWORT
Buddy explains!

The straight part
We know that "ersatz snuff" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ersatz snuff = sneezewort.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 SNEEZEWORT mean?
SNEEZEWORT noun- Achillea ptarmica, a hardy flowering plant, poisonous to cattle, sheep and horses, but with various herbal applications in humans.