the only possibiity I see here is him makeoffer 99$ and u by mistkae acepting it.. in which case it'll still say original 199$ bin price on the pic you showed.
otherwise its a afternic bug that u need resolved. but they rarely make sale mistkaes like this.
as you clearly see, afternic is not giving you 79 on a 199 sale. but 79 on a 99 sale.
afternic has a bin sale system across many networks.. if you change your bin, it can potentially take a long time (or at least not be instant) to change the bin across all platforms.