Many players simply don't know what to expect when they pick up their racquet(s), so this is an example of what to reject!
This image is poor, but it gives you an idea of the lack of commitment, or understanding, or proficiency of the person that strung the racquet. If this is what they think of your racquet, reject it!
Will the knot come undone by itself? Probably not but this does not represent a quality finished product. Reject it!
The image below is the string bed of the racquet with the Very Bad Knots.
It is difficult to see but the string bed is not uniform, nor are the strings straight. This racquet needs to be rejected!