Is it ethical to deliberately utilize a set of people to advertise for a business?

For instance, is conscious word of mouth or placing a group of people in the shop to attract attention even though they are not there for shopping unethical?

I believe customers today are savvy and know an authentic brand when they see it.  Word-of-mouth marketing is a compelling way to build your business and people often go to trusted sources like their friends and family for advice on which products and services to buy.  If a celebrity is spotted and photgraphed wearing a cool shoe or new pair of sunglasses, for example, and that shows up in People Magazine or on the internet, interested consumers will take note and be motivated to buy. That is much more credible than a paid advertisement because the consumer believes it must be truly cool if they wear it by choice (even if it was a free gift from the manufacturer).  When marketing to teens, for example, it can be very persuasive to have a group of influencers wear the product to set the trend. But they must truly believe it is worth wearing to convince others to buy it too.  So my advice is to leverage word-of-mouth marketing, but in an honest way with consumers who truly like what it is you are selling. If they don't, it will backfire and end up diluting your brand ultimately.  It is good marketing and good business.  Good luck!