In my experience with a large UK airline, the captain’s decision is final and there is no jeopardy for a decision taken in good faith. On my command line-check, I discovered that the aircraft had been cleared to fly without a certain required action having been carried out at base. I declined to fly until the correct action had been taken, which delayed the flight. I passed the check-ride!
Conversely, I was given an aircraft down-route, that had been “snagged” for ‘seat-belt signs will not extinguish’. This was not in the MEL and was theoretically a stopper that would have required a new switch being flown out to the Caribbean. Further discussion disclosed that the part had a 30-day delivery lead-time!
Much as I fancied a month on the beach, I couldn’t see any safety issue with getting airborne, so the snag was signed off as ‘ground tested, no fault found’ and it (surprisingly) recurred at top of climb!
Many ways of skinning a proverbial cat.
Mog