[izzy]

If I make use of another person's serial number, can I then get in trouble if they one day decide to use it to for instance repair their pc and realize that another person (me) had been using their SN?

Not really in trouble, but the other person might get ben dovered .
If the company realizes that the SN has been used by a different person, they might be lenient to send out the rma to the person.
But that's the responsibility of using SNs.

But the person whose SN got taken advantage of could, I imagine, easily proof that he was and still is the rightful owner by for instance showing proof of purchase or showing his pc with the SN attached to it, I think he pretty easily can convince the company in this way that his SN was used, without his consent, by another person.

What do you think?

in all honestly ill put it bluntly who cares they arent going to look for who used the s/n (as long as its not too expensive being over 1000) also nothing will happen to you as youll be long gone if you are really that paranoid use a re ship or when you se use a fake name as they cant prove anything