The signed list and the captcha check.
Two checks confirm you are on a genuine Awazon mirror.
The login prints the market address near the captcha. Compare it to the address in your bar. A clone can copy the shop-style theme in minutes, but it cannot easily serve the correct address in the captcha while sending you to the wrong one, so a mismatch gives it away. Run this every session.
Awazon signs its mirror updates with a PGP key. Verifying the signature proves an address came from the market. The mirrors on this page are checked against that signed list.
Awazon