Proof of Funds for a Wholesale Deal

[Daniel Johnston]

If a wholesaler is not doing a double close (which I understand is extremely rare to do anymore), do they always have to show proof of funds to the seller or can they assign the contract and use the end buyer's funding as the proof of funding. I'm getting started and I'm trying to figure out if I will need to speak with some hard money lenders as well. Any help would be awesome!