Good hairdressers sell themselves, not hair products
Most clients believe they can find the products you used and reach the same results that you gave them while providing a beauty service, so avoid promoting products that your clients may not need.
Ask what products he or she uses before pushing them something that will be able to replace your own skills. Mind your client’s financial situation and offer products in accordance with their budget. Do not insist on buying new stuff, if he or she already uses good products.
You may suggest him/her bringing their products so that you can give them some advice on how to use them. Such customized service will help you to make your client trust and respect you.
A lot of women keep dozens of various bottles and tubes of unused or partially used hair products. In this situation they don't need to buy more stuff, however they may want to get some guidance on getting the best results using their products.