You may be surprised, but not in the way you think. The taxes and fees are probably just baked into the rate since it's an all-inclusive deal. You should be fine there. Where the surprise may come in is if you have an accident with the rental and then try to collect on the LDW and/or 3rd party liability. Once a claim has been opened, it will be pretty easy to see that you misrepresented your country of residence and Avis will see a way out of any damage claim.

The rental companies may be incompetent sometimes, but they're not stupid--they know what folks do. It's probably not worth them policing it in most cases where there is no claim--no harm, no foul. However, if you have a major accident with a not significant claim amount, they will check for these sorts of things. If they can find a way to get out of paying and forcing you to pay instead due to a misrepresentation or violation of their terms of service, they surely will. To put it another way, that "free" LDW/LIS you got is probably worthless.