So I can almost guarantee that you have been told at-least once that non-professional products are bad. Yet, have you even been told why?
Lets break it down.
Professional products are gentler, more concentrated, and contain no bad stuff.
Superstore products (Target, Walmart, Sally's, Yes even Sally's) are often diluted, low quality, and if you see a professional brand in stores do not buy it. Reason for that is, "professional" products sold in big box stores are either knock off, or black market/stolen products.
What is the bad stuff: Things like parabens, sulfates, silicone, alcohols. There are other poor quality ingredients out there but I am going to focus on these.
So parabens, these are synthetic preservatives placed into many cosmetic products. They are known to cause skin irritation in some consumers, and have even been found in some breast tissue. Realistically, they are mostly used to stop bacteria and mold from growing within the products on the shelf. Yet more often than not they need all this because it is a low quality product, and parabens are are cheap way to extend the shelf life. Avoid them, they are a sign of trash product.
Sulfates are next. These are harsh stripping detergents that give you that lather. It is derived from mineral salts (which you can imagine, are very drying.) The most common are Sodium Lauryl Sulfate (SLS) and Sodium Laureth Sulfate (SLES). Why are products using these things? They are cheap, and take up space. They also cleanse like crazy, BUT they are stripping away your natural oils as well. So you are left with dry hair + scalp that over produces oils to make up for the oil you are stripping away. This will also take out your color! No bueno.
Silicone! So this may be a familiar word because this is a type or rubber. That does not change because it is in hair products. So basically when there is silicone in your hair products it literally coats your hair in a layer of it. Silicone is a chemical, the only way it can fully get out of your hair is by cutting it out. There are clarifying treatments you can do to help reduce the impact of silicone, but it is not a cure. If you see somthing listed with "cone" in the ingredients, you should steer clear.
Last up, Alcohol. This is a tricky one, There are good AND bad alcohols. The bad alcohols are very drying and can strip out vital moisture. Good alcohol helps combine oil and water so it can be absorbed. The good alcohols are "fatty" and are more oily.
List of bad alcohols: Ethanol alcohol, Ethyl alcohol, Propanol alcohol, Alcohol denat, Isopropyl alcohol, Isopropanol alcohol, Benzyl alcohol
Good alcohols: Cetyl alcohol, Cetearyl alcohol, Stearyl alcohol, Lauryl alcohol
The other part of poor quality products is you're not really getting the "good" ingredients like you would in professional products. That pretty bottle of Suave might say "jojoba oil" on the front, but you're not actually getting that much in there. It is basically a single drop vs a entire 2 liter when it comes to supermarket vs professional product. Even if that Suave might have a fancy oil in it, the amount of build up it places on your hair stops any of that oil from ever even getting into your hair. It is also going to be very watered down so you need about 4x the amount of non professional product vs professional products. So you're not really saving money, It's just not worth it.
If you are looking to buy good products, get them from your local salon (best option as you will help support small business), or Ulta/Sephora are also acceptable places to get products from. Those are the only retail stores I will recommend.