The answers you have received on this are somewhat missing the point. Your comment was "What percentage will make them interested enough to show their buyers?". Therefore, the question is just how much do you want to sell the property and how easy might it be to move? That will always determine the commission to attract a buyer's broker. Anything over the 3% buyers side is extra incentive. Frankly, 6% is not out of line for a harder to move property. (Even more in some cases).
The real question is at the price you are offering, what commission can you afford to pay and still leave something on the table for yourself?
Onward and Upward!
Rob Baird, firstname.lastname@example.org
May 8, 2012