Final answer:
A low bid amount can lower an ad's chance of being displayed. High-quality design, targeted keywords, and relevant landing pages usually improve ad performance. In advertising footwear, not all pages will necessarily display the ad as relevance and targeting are key.
Step-by-step explanation:
The factors that can lower an ad's chance of being displayed include a low bid amount, among other aspects not listed as options. A high-quality ad design, targeted keywords, and a relevant landing page are all factors that typically improve the performance of an ad, making it more likely to be displayed. In the context of advertising footwear, even if you have 20 pages to place ads on, it's not guaranteed that all will advertise footwear. This is because advertising is often targeted to specific audiences and the content of the landing page needs to be relevant to the product in question (footwear) for the ad to perform well and be displayed more frequently.