EVERY MONTH THERE'S A FREE RANDOM PARCEL

So my mom bought this big kitchen storage worth 3k after that the seller sent her a free charger, we thought it was just a nice gesture to thank my mom, and my mom thank them through shopee chat. After a month they sent another one, same charger. Then after a month they sent another, but they were all free, all paid. It happened 3-4 times and we love free stuff. After the charger, they sent another free parcel, which was a window cleaner solution, they did it for 3 months, I think. We were all so confused why this seller keeps on sending free stuff. After the window cleaner solution, it was a plain cardboard piece, like just a small piece. We thought it was a prank but didn't mind it cause we didn't pay anything. Again, it happened every month, now it's December 31 and we received it again. So the question is? Why? I was about to take a photo of the parcel that just arrived but my dad threw it.