Hi gavra_at_work.
Your response is putting the cart before the horse and does not apply to this conversation, as I see it. Nor is your quote a contradiction to what I said.
Who would want to give to someone collecting ALREADY determined to be a fake?? The gemara you provide is based on that exact situation, and in that case, obviously, your response is correct
The situation discussed here is if you SUSPECT someone is a fake. They are not proven to be a fake. How would you know if they are a fake?
The gemara you provide does not say anything about giving or not giving to someone you suspect MAY BE a fraud.
The point of the shiur I heard, to me, still remains valid.
If you want to clarify what to do if you think someone collecting MIGHT BE a fraud, please do.