I have done it with both of mine and it is great, money wise.
I don't live in "Sue the pants off of everybody when you have screwed up and gotten yourself hurt" land, so liability is no problem.
They sign a contract stating that they have read and understood the user's manual and any damage to the machine is on them, including dulled knives.
Never had a problem in the 10+ years I've been doing it.
I do give people a talk through when they pick the chipper up or I deliver it.
One thing I say is that it comes with new knives and I'll open it and check them when it is returned.
Also that chipping that last wheeelbarrow full of small stuff+dirt will probably cost them $100 since that is what ruins the knives.
I've had one stupid game reserve hunting guide ( Stupid kinda comes with the territory with those, don't get me started) run a bunch of wire fence through it.
At first he wouldn't admit it, but once he had thought about how many of the people he works with I know and would tell the story to, he paid up for the damage and meekly asked if we could kinda start over.
So I never told the story to anyone.