We use historical prices and variations in price to define which prices are significantly lower than what would be corcerned 'normal', 'average' or 'median'.
Normally routes with high competition amongst airlines have lower prices.
We do, actually. But scarcely. We however think low cost airlines are pushing air travel in the wrong direction, with agitated and anxious travelers and airline employees.
The faster the better. Although, if you're flexible in your travel dates, you don't have to stress. Every deal shows a expiration date. This date is found in ticket conditions and defines the end of the sale period. Although it's possible prices stay available, it's better to make quick decisions. If there's a good price available in your preferred travel period, book it!