It seems safe as long as you don't do RM*T or anything. and even if he buys your item at a high price for the reason of collecting it, let it be, maybe his intention is really to collect it or our perception is too far-fetched. The important thing is that as long as STS can access all purchase history on all accounts, I think it's safe because I used to think that too, I was afraid, because I once had an item that was offered for 70m even though the price when I bought it was only 15m.
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