2. Why use the Bitcoin blockchain? I can understand using it as a payment system, but there are other blockchains with more extensive smart contracts and lower fees that would serve your database purposes better.
I don't see them as really that stable, and maybe in the future they can change easily making the code outdated.
1. How are you going to mediate fraud/abuse/other problems when everything is so anonymous?
Account1 locks "value_of_product"+"penalty" amount of sats
Seller just now sends package
If problems account1 (the one who needs to send package to buyer) lose the "penalty" and it is given to "escrows" who decide his fate. (It's much more complicated than that but to put it simply it's this)