Why buy good quality beauty & hair care products? The short answer is we spend a lot of money styling and coloring our hair and to make the color treatment last longer and look better for longer we need to use good quality Hair Care and beauty Products.
Salons will be your best bet for good advice in this area as the stylists know from experience what works for specific hair types.
Some nice supermarket hair care products can mimic salon products, though the ingredients probably won't be as high quality (or as highly concentrated). That's why their ingredients labels are always so small.
The reason why you only find specific hair care & beauty products in a salon is because it has been approved by the professionals who work at the salon. If you want your hair to be the best quality with longevity, then I would invest in a salon quality hair care product."
Normally you would also need to use twice as much of the supermarket brand shampoo or conditioner than a more highly concentrated salon brand. This in the long run means you don't save anything anyway.
Overall salon products are always far more superior.