Well, you can't block people from replying to your posts or tagging you in posts for the entire Nostrverse to see. That has certain consequences.
If you scam people on Nostr, you're going to get called out on Nostr and labeled a scammer.
On the other hand, if you're doing honest business, people will say so as well.
For selling physical goods, the burden of trust is on the buyer to trust the seller. The buyer can send sats instantly, but has to wait for the seller to ship them their item.
Sellers won't get very far on Nostr by scamming people. Your reputation on here is permanent.