I am not exactly sure but one possible way could be,asking an additional pay out on top of the prepaid rates.I say that because i have not taken a prepaid auto @ Chennai Central for a long time so i am not exactly sure if that happens down there but i am pretty sure is that the autowalas @ Central are highly reluctant to take a pax to Egmore for a throwaway price.They want some additional add ons along with the actual fare but there is one incident that happened to me when i was in Kolkata last year.I was going from Howrah to Esplanade and i got myself a prepaid taxi,everything was fine but as i was getting down @ Esplanade,the taxi driver asked me if i was willing to pay something extra.......so,may be that's one thing that could happen.He was pretty vocal in his demands not aggressive or assertive...
more... but with a strong tone nevertheless but i declined and that's the end of story back then.It cost me around INR 70 or thereabouts if i remember correctly from Howrah to Esplanade and he wanted a few extra bucks to go on top of it.