So, say Avis sent me a text say my car number is 209. I don't like it, so I go to Select and Go lot and drive another car. My question is this:

1) Say I reserved under Compact
2) Avis assigned me a Full Size that I don't like
3) I went to Select and Go and picked another Full Size

Would Avis count me as "upgrading on my own" and charge me the difference, or Avis will be smart enough to know they've already upgraded me to Full Size so by picking another car it won't increase my rate?

Thanks