I subscribe entirely to Chilli Monsters point.
The planes might be sat idle in the hangars but the majority of a/c owners would rather have that situation when they are busy doing other things than worrying about a stranger bashing around the countryside "hours building".
When you own a plane you make every endeavour to look after it as not only do you rely on it to keep you in the air, you also try to minimise those annual and six monthly bills.
Once a "hirer" has finished with a plane is he going to clean the bugs off, leave it as tidy as the owner would inside, fill it with fuel, check for any signs of leaks etc etc?
I doubt it.
I know a person who was recently approached by an hours builder who wanted to rack up some hours in his Saratoga. The a/c owner took the request almost as an insult and politely explained that £500 per hour would just about be enough to stop him worrying himself sick when he knew that his plane was in the air with someone else at the controls.