Reasons as to why a reputable merchant would be selling a knock-off handbag as real?

I am not surprised you saw it in Marshalls. I have seen a fake Dooney & Bourke on the racks at Marshalls and brought it to the manager's attention. 1/2 hour later, I saw a clerk put that fake Dooney right back on the racks. These discount retailers buy overstocks and unsellable merchandise from retailers at BULK rates Marshalls does not pick and choose what overstocks they buy.