Regardless of very individual personal preferences, you've most likely noticed that people tend to wear clothes that are similar to what their friends are wearing and the group that they are part of. Business people of a company or area, kids and Goths are all good examples.
Working in Sydney, I've found that business people are wearing far more informal clothes to work than they used to . I used to meet with clients in business pants and shirt and tie, only to discover that I was over-dressed - the business owner or director was wearing jeans ! So I've now conformed by wearing similar casual clothes when I go to talk to a client. And I've observed that this simple agreement of similar-style clothes helps smooth-out initial meetings.
Gaining agreement from customers that what you are providing is what they in fact want to buy, is a similar thing. A mannequin display, both female and male mannequins should duplicate how people think they should look. So it's important to stay very conscious of the people in the locality of your shop and in the market segment you're promoting to, and what they are thinking.
Another point to be aware of is that about 80% of your customers live inside of a 5 mile radius of your shop. These are the people its worth surveying or otherwise finding out about.
Opinion leaders in fashion, such as celebs, should also be kept track of and its also really good marketing to make a display that's out-of-the-ordinary to catch initial attention, as long as it stays within your market's consideration of correct aesthetic style, because the manequins are copies of real people.