A.:
On Extreme Homemaker - it is all free - however - the people are assessed taxes on the new value of the home. If they received the deed to the home - most had to take a mortgage out to pay for the taxes. In one case, the children sued the adopted parents (I believe).
In "Yard Crashers" - it's all paid for but it is considered income and you are liable for taxes. I don't know the tax rate.
In some shows - where they sell items of the homeowners - I think it's all good. Like the old Nicey Nash show - messiest house? I think it was all good because the people used their items in exchange for services.
I don't know. You can check on the HGTV website to get the details if you get to be on the show. ALL of the implications are there...just like on The Price is Right (my best friends mom won a van on there back in mid-70's) - you have to pay the taxes on it when you take possession (at least she did back then!! Good thing they had the money!!! :) )