Software engineering has no qualification standards, and the people who need developers are very poor at identifying/recognizing what a great developer is. The result of this is that there are legions of terrible developers. Our industry is packed with developers who have no business even being in the industry. It’s common to find resumes overflowing with acronyms and claims about their knowledge, which more often than not are extremely exaggerated or just outright falsehoods.
If after you interview a candidate you find that you aren’t completely sure about them, don’t hire them. If you can’t tell if they are good or not, don’t hire them. If 2 out of 6 people on the interview loop are either ‘no’ or ‘maybe’, don’t hire them. The consequence of letting a bad developer in the door is far greater than maybe missing a good one.