What is the BIGGEST mistake made in marketing? This mistake is made by 99% of the companies marketing products or services… The biggest mistake in marketing - and not just direct marketing, but any marketing - is made by people who spend a lot of time, energy, and money on an ad or an inquiry-generation program. When they receive the highly qualified lead it brings in, they send a brochure and a letter. At best, they call about a week later. When a sale is not immediate, they hang up, and they never call back or send another letter. They assume their campaign failed. What a mistake. A single letter and brochure is not a campaign. A campaign is not a single effort of anything - why do you think they call it a campaign? A campaign is a sustained effort over time…. The biggest mistake made in marketing is not contacting a well-qualified buyer, who has expressed an interest in your product or service after the first mailing, a second time with harder-hitting additional marketing material or letters.