dt1 wrote: You can demand anything, but the store does not have to agree to it
Here, the Consumer Act of December 25, 2014 plays the main role.
The replacement for a new and defect-free one is listed as the first in the Consumer Act (resulting from the provisions on complaints) - and the customer has the right to demand it, referring to its provisions.
If the customer's request (replacement for a new and defect-free item) cannot be met, the store is obliged to propose a different solution to which the customer is NOT obliged or forced to agree and can still insist.
It is the customer who indicates what he expects from the seller (replacement with new and defect-free goods, price reduction, repair).
dt1 wrote: It must be a warranty
It is better to use the determination of non-compliance of the goods with the contract.
dt1 wrote: It is not always better. For example, the manufacturer can provide a 3-year warranty (and this is the case with current TPLink products), and the warranty can only be used for 2 years.
It is more favorable in the first 2 years

(when it comes to the manufacturer's warranty for a period of 3 years).
For the first 2 years, it is protected by the Consumer Act and the provisions of the Civil Code.
When using the warranty, you have virtually no rights and you are forced to agree to the manufacturer's conditions.
dt1 wrote: So if the router is at least one year old, then its current owner will be obliged to prove that the defect existed at the time of purchase (which in my opinion could be difficult and even quite expensive, if feasible, if you find an interesting seller - here warranty can sometimes be easier to fulfill).
I have not heard of a coincidence that the store rejected the customer's request and demanded to prove that it was to blame for damaged equipment over 12 months.
The manufacturer's service will replace it just like that and will not examine the equipment in depth - if it gets there, they will check the cause of the damage and it may be uninteresting then?
Very often, the seller does not give the equipment to check anywhere, just exchanges the customer and that's it - then he reports the pre-sale damage to the manufacturer of the equipment and the manufacturer replaces it with the store immediately for a defect-free item.
I have used complaints many times (and practically only from it), the provisions of the Consumer Act have never failed me (maybe once, but the store heard that I was going to the Consumer Ombudsman and immediately changed its previous negative position

).