Seriously? OMG! I re-write the sentence and please read it carefully because you totally miss the point : No one want a market stored in the blockchain! You pretending to be annon and you want to store those data on a blockchain ...
Yah, it is not a good idea to store the buyer and/or seller's personal information on a public blockchain but that is not what is being done here.
All that is stored on the market blockchain are the item for sale, public key of buyer, public key of seller, date sold, and purchase price, NOT any personally identifiable information like buyer's name, shipping address, etc... I am not sure how you would resolve a public key (likely stealth pubkey) to a real person. How does this compromise anonymity more than any other form of crypto?
Vendors and buyers keep feeding the Amazon and eBay machines. Let's give them more money to use their insecure web sites. Do you know how many people hack into eBay, PayPal and Amazon accounts and steal personal information including money because of their lack of security? They still don't use 2FA.