Theres a difference between saying "renovate my porch for free" and adding "...and the winnee gets to renovate my dusty, moldy, wet, crumbling, spider and rodent infested basement as well, totally free of charge!!!!"
I doubt that not offering a prize at all would have caused more than a slight grumbling at worst. Trying to offer advertisement as a reward though is rightfully frowned upon.
Yeah actually, I can see where you're coming from there!