This script is pretty nice but I've got a few concerns, especially relating to the TOR aspect of it. Please correct me if I'm wrong. Also I have some recommendations:

1) It's not very well optimized for TOR in terms of anonymity. I can easily see what webserver and OS you're using just by causing a 403 error. (nginx/1.10.3 (Ubuntu)). The whole point of TOR is to be anonymous and this could easily deanonymize you. Should it not redirect you to a custom error page which hides this information?
2) There's no search function? On a marketplace I would think that this would be a basic feature that would have been implemented.
3) There's no sub categories. Again, I feel like this should be a basic feature that it should ship with?
4) Why is the "My Products, My Sales" and "Feedback Score" showing on a buyer's account? A trust rating for a buyer is redundant isn't it? The feedback doesn't show anything when logged in as a buyer, even after leaving feedback for a vendor. Also, I think that "My Purchases" should not be visible to vendors since they should only sell.
5) I also think the "Profile Description" should be hidden for a buyer's profile since they only buy and don't sell anything.
6) When you reply to a message, it should automatically fill in the Title from the original message.
7) The possibility to see the prices in a fiat currency (like USD) and then convert it to BTC when making the purchase. I think it will be handy with the BTC volatility.

I hope you see these comments as positive feedback and improvement recommendations. The script is very good, but I think these smalls things might make it even better.
Good job