I am not a lawyer, and none of the following should be seen as legal advice.
While it is always best to assume every image has a copyright....
In your scenario... traditionally if you are selling a product, there's generally no harm in using images of that product to assist in the sale. But even then photographer copyrights should be considered. Images of products may not only contain copyrighted material within the photo, but the photo itself is probably also copyrighted by the photographer.
Just blankety taking images from other web sites is a poor practice in general and will customarily just get you into trouble. However, many manufacturers or distributors will actually provide resellers with product images. You can check the product manufacturer's web site for a "press" or "media' section. There are often downloads provided in those areas.
I don't know hairdressing.. but as an example, General Motors has a special web site known to GM car dealers where the dealers can download high resolution images of the cars and products for ads, etc. I've done work in the past for a GM dealer who provided me with the web site and log in details so I can get product imagery.
In addition, few manufacturers will take umbrage that you are using their images to sell their products. They want their products to look as good as possible wherever they may be displayed. In many cases, they may prefer you use supplied images rather than use your own.
Customarily you would include a disclaimer in the footer somewhere:
The product names, company names and product images used on this web site are for identification purposes only. All trademarks and registered trademarks are the property of their respective owners.
Note, I am referring to images from the manufacturer's web site, not from competing businesses. If you are building a site for "Bob's Hair Styling" it's unethical to take images from "Kate's Hair Dressing" for your use. Stick to the manufacturer... if selling Paul Mitchell products, check the Paul Mitchell web site for available product images.