Total scam - you don't need to use them and they have insanely high change fees. Just book directly with the rental company providing the car. Argus is nothing but a middle man that provides no value to you (and in fact may end up costing way extra). In my case I wanted to change my reservation by two days for the same total number of days (start two later, end two later) and was changed an 'amendment' fee that was only 10 USD less than the total value of my original booking. Basically, I paid about twice what it would have cost me had I just booked through the end provider (Sixt) and used their flexible book option (which is a modest extra $2/day rather than the huge fee Argus charged despite my very small change).