The most common and most likely answer to this crossword clue is the 7 letter word DROPPER
I've seen this crossword clue in The Times
D
R
O
P
P
E
R
Buddy explains!

The straight part
We know that "Careless type" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case careless type = dropper.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 DROPPER mean?
DROPPER noun- A utensil for dispensing a single drop of liquid at a time.
- One who drops something, especially one who drops a specific item to cause mischief.
- A software component designed to install malware on a target system.
- A fly that drops from the leaden above the bob or end fly.
- A branch vein which drops off from, or leaves, the main lode.
- A dog which suddenly drops upon the ground when it sights game.
- A person who uses fraudulent cheques.