Allow sellers to offer sales on their gig extras or multiples. (ie. reg extra = $15, today only = $5. Buy 3, get 1 free)
yah that would be a great idea.
or why dont you just promote it to your buyers that you are giving away free info, service etc. this way it will be out of the blue and the buyer will be excited. you can do it for new buyers that contact you. it will be an incentive for them to come back to you again.