The most common and most likely answer to this crossword clue is the 5 letter word WARES
I've seen this crossword clue in The Daily Telegraph
W
A
R
E
S
More clues leading to the result WARES
Buddy explains!

The straight part
We know that "merchandise" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case merchandise = wares.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 WARES mean?
WARES noun- (usually in combination) Goods or a type of goods offered for sale or use.
- (in the plural) See wares.
- Pottery or metal goods.
- A style or genre of artifact.
- Crockery.
- Goods or services that are for sale.