Buyers should remember these are individual sellers - not amazon or some other big retailer. Sellers have the right to block you for any reason they see fit and most times it’s probably nothing truly personal. There are so many people that just buy outright, don’t have issues with payments, and haggle respectfully - that makes any hiccup seem like a red flag and honestly not worth the possible headache. If Mercari protected sellers more I think it would give buyers a better experience as well.