seller, cellar

Seller or seller means the person or party who has offered something for sale--
If you have any questions about the item, contact the seller directly.
The seller says he can wait until Friday for payment.

Cellar or cellar ( rhymes with seller ) means a basement or underground room--
We left the windows open to air out the cellar.
Don't put the books in the cellar. They'll get musty.

Now that you know that, you can say--
"He has a cellar full of old stuff. He ought to become a flea market seller.

Note--"cellar" is also an old-fashioned word for a type of dish or compartment, as in the expression "salt cellar" , meaning a dish for holding salt, instead of the more modern salt shaker.
A person who sells salt might be called a "salt seller", but that would be unusual.