What if I ask customers to send me empty bitcoin paperwallets (BitAddress.org) ?
You should not do that, the empty paper wallet would need to contain the private key for the public key. Before the empty wallet is sent your customer can copy the public and private keys and send the funds. He could then import the keys back to his wallet and take the funds back.
All you need to do to get your funds into your wallet is look for the import/export tab in your wallet, copy the public key and private key in the appropriate section and there you go. That's it.
With high value items there is no need for you to use any special system. Sticking with BitPay and Coinbase is something easy to do. There's also stripe to look at.