The Avis small print on rental contract states the following (BTW - even if you only have ONE single cashless transaction, you're opting into a $3.95/day convenience fee for each day of your rental). How would a person even override the installed transponder with the one the renter owns?

If you do not pay cash for tolls, you automatically opt into our e-Toll service, pursuant to which you agree to pay us or our toll program administrator, with whom we will share your credit card/debit information, for all tolls incurred during your rental and all related fees, charges and penalties. Under the e-Toll program, once you pass through an electronic toll, you will pay a convenience fee of $3.95 for each day of the entire rental period, including any days on which e-Toll is not used, up to a maximum of $19.75 per rental month, plus incurred tolls at the maximum prevailing rates posted by the toll authority. You can avoid the convenience fee and any other charges by paying the toll in cash, using your electronic toll device, or avoiding any cashless toll road or passage. Please be aware of roads that maybe "cashless tolls" and drivers on these roads are not able to pay cash once they have entered these roads. You automatically opt into our e-Toll service program and will be charged $3.95 for each day of the entire rental period, including any days on which e-Toll is not used, up to a maximum of $19.75 per rental month, plus incurred tolls at the maximum prevailing rates posted by the toll authority. The charges may take 4-8 weeks after the rental to be billed to your credit card/debit card on file.