You can use either secondhand or used. However, secondhand is more commonly used when we talk about clothing. We say 'secondhand shops', if it is a clothes shop we might say 'charity shop'.
If you buy and sell secondhand or used goods, your job can be described as 'buying and selling used goods.
I buy and sell secondhand/used goods.
私は中古品の買い取り・販売をしています。
"secondhand" または "used"のどちらも使うことが出来ます。（[中古](https://eikaiwa.dmm.com/uknow/questions/1738/)）
ですが、[洋服](https://eikaiwa.dmm.com/uknow/questions/36071/)などの場合"secondhand"の方が一般的によく使われます。
'secondhand shops'と言いますが 'charity shop'と言う事もあります。（中古ショップ）
中古ショップで中古品を売り買いするのが仕事だったら、 仕事を'buying and selling used goods'というよう表現できます。
No ...it's not secondhand! I only sell previously owned goods;-)
Secondhand has some negative connotations ;-D Along with... "used goods"!
We may therefore wish to employ a small euphemism: Such as ..."Previously owned"
"No ...it's not secondhand! I only sell previously owned goods;-)"
「secondhand」には少しネガティブなニュアンスがあります...「used goods」もです。
もう少し遠回しな言い方のほうがいいかもしれません。例えば...「previously owned」。
"No ...it's not secondhand! I only sell previously owned goods;-)"
(「secondhand」じゃないよ！「previously owned goods ([中古品](https://eikaiwa.dmm.com/uknow/questions/1738/))」を売っているの)
I make a living by buying and selling previously owned items.
My business consists of buying and selling hand-me-down items.
To explain that one buys second-hand items you may say the following;
I buy and resell pre-owned items.
I make a living by buying and selling previously owned items.
keywords:
second hand: Something that was previously owned by someone else.
previously owned- Not new, something previous used or worn by someone else.
hand-me-down:
A garment or other item that has been passed on from another person.
中古品を買う人を説明するために、下記の通り言えます。
I buy and resell pre-owned items.
中古品を買い、再度売ります。
I make a living by buying and selling previously owned items.
中古品を売買して生計を立ててます。
second hand：他の人が以前所有されてた物
previously owned：新品ではない、他の人が以前使ってた、または着てた物
hand-me-down：他の人からもらった洋服、または物
Buying and selling secondhand items is a vast industry in the UK. There are many shops in the high street dedicated to selling, for example, secondhand furniture. Charity shops in the UK are everywhere, selling items donated by members of the public to raise money for good causes. What is most important is to describe the type of secondhand good you deal in. For example you may be a 'secondhand car dealer.'
If you have a shop you could tell your friend that you own a thrift store. This is a store that buys and sells used items. Or you might tell your friend that you buy goods at a thrift store and then resell them.
I hope this helps.
I deal in secondhand goods.
→中古品の買い取り・販売をしています。
I buy and sell secondhand goods.
→中古品の買い取り・販売をしています。
中古品の買い取り・販売をしていることは、上記のように表せます。どちらも同じ意味です。
「中古品」は「secondhand goods」などと言えます。
「deal in ～」は「～の取引をする」という意味です。
「buy」は「買う」、「sell」は「売る」という意味です。
ご質問ありがとうございました。
Items that have had a previous owner are called used. There are different grades of used items and different terms when it comes to a specific field. They can be refurbished which means that they have been fixed to work like they are new by a factory or repair man, especially with tech gadgets, machines etc. Second-hand clothing is called just that and are sold at thrift shops along with different types of accessories. Clothes and any item can be given instead of purchased. These items are called hand me downs. Also, a rare valuable such as jewelry or artwork may be referred to as antiques. These items are usual sold at auctions.
前の所有者が持ってた物は、usedと呼ばれます。中古品の等級は様々で、特定の分野になると異なる表現があります。中古品は、修復調整されます。これは、工場、または修理工によって特に技術機器、機械装置等を使って新品のように直すことを意味します。
second-hand clothingと呼ばれる洋服は、リサイクルショップで異なるタイプのアクセサリーと共に売られてます。洋服や物は、購入すると受け取れます。これらの商品は、hand me downs（お下がりの洋服）と呼ばれます。
また、宝石、あるいは芸術作品のようにレアで価値のあるものは、antiques（アンティーク）と言います。これらの商品は、通常オークションで売られます。
To pay money for something you want is called to buy, to get money for something you own from someone else is called to 'sell'
A thing someone else has owned before is called 'used' or 'second hand'
I buy and sell second-hand goods.
私は中古品の買い取り・販売をしているよ。
As for work, I buy and sell second-hand goods.
As for work= 仕事は〜
他に：used goods (中古品）
I buy and sell used goods
ご参考になれば幸いです。
イギリス 
南アフリカ 
アメリカ合衆国 
日本 
オーストラリア 
