I have seen a few referendums in the past:
- The Turkish presidential system referendum with 51.41% for the new system. Source
- The Brexit with 51.89% for leaving the EU. Source
- The Irish abortion referendum with 68% for allowing it. Source
- The Swiss "Billag" vote for publicly financed broadcasting with 71.6% for keeping the current system. Source
- The annexion referendum on the Crimea with 95.5% to join Russia. Source.
The first two ones are awfully close to a tie, and that makes it problematic. When the result of a "Yes or No" referendum end that close to 50%, I would argue that the referendum asks the wrong question.