Flight search engines cannot realize the true impact of local events; they only show a fraction of the information needed to assess risks.
A cheap flight to Munich during Oktoberfest does not guarantee that you will find affordable accommodation, even with flexible dates.
The problem is not what these tools show, but everything they do not show, such as transportation saturation or local disruptions.
Ignoring these downsides can turn a "good deal" into a real headache, with no fail-safe for your stay.
Caution is advised to avoid surprises that could ruin the entire trip.