The world is one huge, competitive marketplace. Your prospects don't need you as much as you need them. You need prospects to become customers and the first step to converting prospects into customers is capture their interest. Woo them in, attract them, gently prod them along. Apparently, some classified advertisers assume that anyone who reads their particular ad is automatically going to respond.
Most ads have no incentive for the reader, no enticement to inspire action, no huge promise.
Inaction is always easier for the prospect. It's called the inertia factor and it can be fatal to your business. This mistake is easily preventable by knowing your audience. The wrong appeal simply won't work. This should seem obvious to anyone who's prepared to spend hard-earned cash on a classified ad, but I see it all the time.