I DON'T think the commission is the FIRST thing lenders go after in a negotiation. Lenders know they are dealing with a real estate agent. Just do not expect to be able to get 10% on a short sale listing. I have never seen an agent be cut off on their commission. That is ridiculous. Know that you might negotiate your commission but you will NOT be left high and dry.
I've put together an e-newsletter all about negotiating and short sales. Check it out.