From what we can see in your photo, it seems that the person wearing the sandal has not a 39 (sample size), but rather a 40 or 41, because foot is quite large and fitting is not right.
What we can tell you is that we already deal this article from different seasons and it's a tested model. We never had problems or claims of this sort by anyone of our customers.
Since it's a PVC sandal with printing, it's not possible to change fitting nor extend the strap on the buckle.