Biggest problem that my friends in marketing/sales explained to me - if there’s no proper conversion from ads to sales, huge problem with bots AND negative targ

Biggest problem that my friends in marketing/sales explained to me - if there’s no proper conversion from ads to sales, huge problem with bots AND negative targeted ads, then it’s not worth it. Honestly, I have close to 0 knowledge in terms of marketing and advertisement, so mostly rely on others’ opinions and tactics.