For the chargebacks bitm, there's this in the
FAQAm I liable for unauthorized transactions made using Google Wallet?
If you would like to dispute an in-store transaction made using a linked credit or debit card in your Google Wallet, authorized or unauthorized, please call us and we will work to resolve the issue. You also have refund or other rights under your agreement with the issuing bank of your linked debit or credit card. Contact the issuing bank and the agreement governing your card account for more information. Many banks apply a $0 liability policy for unauthorized use.
So, not completely clear whether Google does it directly or if you just deal with your credit card company or bank.