Verification is done by assigning a slightly different payment amount to each person. For example, if you are charging 0.00015 BTC, the amount 0.00015001 and 0.00015002 may be used to distinguish two payments. These amounts are cycled every ~15 mins.

Edit: Also, I may add support for BIP32 master public keys in the future. This would allow derivation of child public keys on behalf of the user, providing a unique payment address for each transaction. This is technically easy to do, the only problem is most people don't know how to access their master public key.