The most common and most likely answer to this crossword clue is the 8 letter word JEWELLER
I've seen this crossword clue in The Guardian
J
E
W
E
L
L
E
R
More clues leading to the result JEWELLER
- Derisive remark about prosperous gem dealer
- Ring salesman perhaps, to scoff, around spring
- Adeptly cutting mock diamonds one sells?
- Taunt about healthy tradesman
- Fit mock rings? He might do
- In France I joined Sam, a dealer in diamonds
- Hector accommodates healthy craftsman
- In Paris I may meet Sam who sells valuable items?
- Mock rings OK, one selling necklaces etc
- Daedalus in Paris with Dickensian humorist and artisan
Buddy explains!

The straight part
We know that "who sells valuable items?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case who sells valuable items? = jeweller.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 JEWELLER mean?
JEWELLER noun- A person whose job is making, repairing or selling jewelry.