FTC policies and guidance
The Federal Trade Commission has a page featuring several 
Guides and Policy Statements. I have summarized items that have to do with hair removal regulation.
For consumers
"Normally we expect the marketplace to be self-correcting, and we rely on consumer choice-the ability of individual consumers to make their own private purchasing decisions without regulatory intervention–to govern the market. We anticipate that consumers will survey the available alternatives, choose those that are most desirable, and avoid those that are inadequate or unsatisfactory. However, it has long been recognized that certain types of sales techniques may prevent consumers from effectively making their own decisions, and that corrective action may then become necessary."
An advertising practice is considered unfair if
- it injures consumers (including financial injury)
- it violates established public policy
- it is unethical or unscrupulous (violates generally accepted business practices)
FTC will find deception "if there is a representation, omission or practice that is likely to mislead a reasonable consumer." If an ad is targeted at "highly susceptible classes of purchasers," the effect on that group will be taken into consideration.
Advertisers, ad agencies and website designers must have a "reasonable basis" for advertising claims before they are disseminated.
Advertisers, ad agencies and website designers must substantiate express and implied claims that make objective assertions about the item or service advertised.
A firm’s failure to possess and rely upon a reasonable basis for objective claims constitutes an unfair and deceptive act or practice.
When the substantiation claim is express (e.g.., "tests prove", "doctors recommend", and "studies show"), the Commission expects the firm to have at least the advertised level of substantiation.
What constitutes a "reasonable basis" depends, as it does in an unfairness analysis, on a number of factors relevant to the benefits and costs of substantiating a particular claim. These factors include: the type of claim, the product, the consequences of a false claim, the benefits of a truthful claim, the cost of developing substantiation for the claim, and the amount of substantiation experts in the field believe is reasonable.
Substantiation investigations will rarely be made public before they are completed.
Statements from satisfied customers usually are not sufficient to support a health or safety claim or any other claim that requires objective evaluation.
An endorsement reflecting the experience of an individual or a group of consumers on a central or key attribute of the product or service will be interpreted as representing that the endorser’s experience is representative of what consumers will generally achieve
Unless there’s adequate substantiation, the ad must disclose what the generally expected performance would be. (i.e. a disclaimer stating "results may vary").
Claims concerning the efficacy of any drug or device shall not be made in lay endorsements unless:
- the advertiser has adequate scientific substantiation for such claims
- the claims are not inconsistent with any determination that has been made by the Food and Drug Administration with respect to the drug or device that is the subject of the claim.
When there exists a connection between an expert endorser and the seller of the advertised product which might materially affect the weight or credibility of the endorsement (i.e., the connection is not reasonably expected by the audience) such connection must be fully disclosed.
For manufacturers, practitioners, advertisers and web designers
The FTC considers web designers and ad agencies just as responsible for claims made in promotional material as manufacturers and practitioners. It’s up to you to determine if claims are substantiated. Knowingly promoting a device with false or unsubstantiated claims violates federal law.
FTC has put together an excellent list of Frequently Asked Questions to help small businesses comply with federal law. Other useful pages:
Source: FTC website