Answer:
Well on obvious reason is that it is illegal to false advertise... there is also a term used in economics called "bait and switch" which is where they advertise an amazing product, but then you go the the store and they don't have it so they show you the "next best"... this practice is also illegal.
There are different types of products which are advertised as high class. These usually are noticed by the consumers because of the title or brand. Examples of which are Apple (phones) and also other products used by consumers. A law was passed to protect all consumers from bad products that may harm that person, and the misleading ads.The FTC passed this law, to keep every consumer safe from things that could effect there life. Dangerous products, and misleading ads can effect a consumer a lot. So, the FTC passed a law to protect consumers to be protected from dangerous products, and misleading ads.
If a claim in an advertisement is vague then it is open to many specific things so a person would not know what the advertiser is talking about.
Unlike advertising and sales promotion, personal selling can respond only to the questions and objections that the copywriter thinks are important to customers. Since the advertisements and the sales promotions are nonnegotiable once out in the media, these are approved by the copywriter and what is allowed and deemed to be advertised is.
When you conduct personal selling you are talking one on one with a customer or client base and can explain the product more in-depth and focus on the benefits for each one verses the overall product to a large customer base.