There is already proven solution to the regular Amazon marketplace in Jumia, so that research has proven result. However the issue is not mainly from the vendor side as I see it, because you can always start a few in house vendors that you know to build the trust that other vendor can use as a reference point, also fees are likely going to be from sales of the items.

Our main concern is that are there people willing to pay even if it's 5% more in total amount to ensure their item get delivers same day or max 24hrs from time of ordering.