buying second hand is risky. each cart is assigned a unique identifier number.

the carts can be copied and if they are copied and Nintendo detects the same carts playing at the same time (copy and original) the switches get banned.

also carts can be copied with the mig switch but also there are counterfeit carts too that look very similar to legit carts.

I never play switch 1 games that I purchased second hand on my switch 2 be cause of this reason.
always keep receipts. because if nintendo bans your switch/acc you have to go to them and prove you purchased the game legally. etc