You could always curse the transaction to failure.
Would your "freinds" not be pretty sore, if what-ever the dealings happened to be, turned out all wrong for them?
Maybe that Owner is a schmuck, who has poor follow up business ethics, to further complicate the deal.
Otherwise, I would chalk it up to a lesson learned in "loyalty", and pursue the means to make your immediate discomfort a launch pad of IN THEIR FACE future prosperity.
You could even poison the well by forcing perceptions upon the friends who burned you.
"I would of given a ten percent discount off of that and beat his price...but, oh well...too late now! Not to mention my excellent service and backing, I hope you get what you paid for! If their is anything I can do to help..."
"I hope you know about this feature... that other guy might not of known about it, but it sure will help you out in the long run. He didn't mention it? Maybe you should go back and request his help, and get yourself what you need. Mention that it should be FREE, due to your troubles, you know..."
Being subtle, and not overt in the detractions of your foe give you the feel and look of the caring professional, minus the blatant bitterness of some-one scorned.
Having a knowing smile on your sinister mug, when people come to you, bitchin' about their good deals gone bad...that is frosting on the cake.
"Create chaos, then fashion what you will from it...Be a god!"