Cryptic crossword clue
Northern Ireland flipping certain to get guarantee 6

The most common and most likely answer to this crossword clue is the 6 letter word INSURE

I've seen this crossword clue in The Daily Telegraph
I
N
S
U
R
E

Buddy explains!

The straight part
We know that "guarantee" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case guarantee = insure.
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 INSURE mean?

INSURE verb
  1. To make a pledge to (someone); to promise, guarantee (someone of something); to assure.
  2. To make sure or certain of something (usually some future event or condition).
INSURE verb
  1. To provide for compensation if some specified risk occurs. Often agreed by policy (contract) to offer financial compensation in case of an accident, theft or other undesirable event.
  2. To deal in such contracts; subscribe to a policy of insurance

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