Many people might have this dilemma. As opposed to the costly Windows operating system, users, developers and businesses tend to use open source operating systems for their computers. Other professionals tend to use open source software tools for their productivity. So, are they using them because it is called "open" and maybe tagged with "free" as in FOSS or maybe someone told them open source is really free?
Open source is a term coined way before computers were made. It takes us back to the early 1900s. Instead of going into history, let us know what Open source really means. "Open source" is a way of distributing source material to a user at no cost. It can be upto the ability of the user to enhance the source material and redistribute or simply use it for his productivity, provided the material is a tool. So, essentially it is a product ultimately dependant on collaboration within the community which makes it better.
Below is a good video on what Open source software actually is.
Today we have many options of choosing software. Some have the name "open source" on it, some have "freeware", and some have "free and open source". We know what open source and free are, but what about the "free and open source". No, it doesn't mean it is free of cost theoretically. "Free" means "Freedom" to use the open code. Open code ultimately is free of cost, so technically it can be free.
Making money using open source products does not put you in any type of patent infringement. The license used might be usually GPL 3.0 or GPL 2.0 under which you are free to use the code or make money by using it or even redistribute and make free copies for others. This also means you can sell the software at any cost you like. You can only make money by using it or selling it. So you got software which is free, and also makes you create something using it and make money which is quite the opposite of commercial software which you have to buy, and then probably pay royalty when you create something with it. Open source is very advantageous and excellent choice, but, then is open source software reliable?
Open source software is usually supported by a "community". It is mostly possible to get answers out of them, but it could be somewhat hard to get silly questions answered by them, as most of them are high level pros and are not messing around. On top of that, it is also not very clear if the software is fully reliable or 99% bullet proof. Commercial software support however is always ready 24/7 for you, because you bought their software and most companies are really concerned about their customers. With a 24/7 support, you are always free to question, get free updates or even get a free replacement of a software provided it is under warranty and the terms and conditions adhere to it.
So, using open source software is somewhat questionable. If you are using it for some productivity, you should use it, but, if you are undertaking a big business and need support, I would recommend a commercial product which is at reasonable price. Commercial products are reliable at most times.