Unless you have an unusual psychological condition, the answer is probably almost never.
Most folks are no different.
Windshield wipers are a perennially neglected maintenance item. Manufacturers almost universally recommend wiper element replacement at least once a year, or even every six months in harsh conditions. A little quick arithmetic shows that at least two-thirds of drivers are likely to be in need of windshield wiper maintenance on any given day. That means that wipers are a natural for legitimate sales and merchandising efforts. Talk it over with others in your outlet, and see if there is a way you can promote wiper blades, refills, and inserts to those who need them.