Ask who is paying, because somebody always is

Free describes what you hand over at the counter, and not much else about the arrangement.

The word free is a statement about one specific thing: no money changes hands at the point of use. It says nothing about who funded the thing, why they funded it, or what they expect to happen next. Sometimes the answer is entirely benign and public. Sometimes a business gives something away because it profits when you later buy the paid version, which is a normal and reasonable trade openly conducted. Sometimes the funding comes from your attention, your data or your eventual inattention. All of these can be acceptable. What is not acceptable is not knowing which one you are in.

The habit worth building is a single question asked calmly before accepting anything: who is paying for this, and what do they get. It takes seconds and it is not cynicism. Public provision is paid for collectively and the expectation is that you use it. A sample is paid for by marketing and the expectation is that you remember the name. A free tool from a company is often paid for by a paid tier and the expectation is that some percentage of users upgrade. Each answer is fine. Each answer also tells you exactly how the thing will behave over time.

The answers you cannot get are themselves informative. If it is genuinely unclear who funds something, if the terms are long and vague where they should be short and specific, if the offer requires payment details for a thing described as costing nothing, or if the pressure to accept quickly is high, then the arrangement is relying on you not looking. That is not a reason for panic. It is a reason to slow down for ninety seconds, which is roughly the amount of time the design is hoping you will not spend.