The most common and most likely answer to this crossword clue is the 6 letter word GROCER
I've seen this crossword clue in The Guardian
G
R
O
C
E
R
More clues leading to the result GROCER
- Shopkeeper sounds more repulsive
- Shopkeeper is more vulgar, we hear
- Concerned with short Welsh dog going around shopkeeper
- Tradesperson is more obscene we hear
- Even more boorish-sounding, the ex-PM, in our eyes
- Reported excessively offensive dealer
- Shopkeeper pronouncedly less refined
- Retailer’s profits, according to rumour, were unlimited
- Fabulous flyer collected by German shopkeeper
- Retailer raised some Pembrokeshire corgis
Buddy explains!

The straight part
We know that "high street trader" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case high street trader = grocer.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 GROCER mean?
GROCER noun- A person who retails groceries (foodstuffs and household items) from a grocery.
- To sell groceries; to act as a grocer.