They charged $187 extra, for that one day I was late (actually a few hours). For the rest of the rental the daily rate was $25. Apologies for not being clear.

"I've never had Avis charge "what they want", just the daily/hourly rate, plus any potential small late fees." Do you consider a $187 (or 7-day charge) a "small late fee"? Me neither.

" if you don't stay within those terms"
I'm not sure what terms I didn't stay within. If someone brings a car back late can they charge whatever they want? Why not $1000 a day?