sales man shows him one and says "This one can cut down 20 trees in an hour, guaranteed!"
"OK, I'll take it." and the man leaves.
He comes back the next day with the chain saw and says, "This only cut down two trees in an hour. I think I need a better one."
"Ok," says the salesman and he shows him another one. "This one can cut down 40 trees in an hour!"
The man takes it and leaves.
He comes back in with the chainsaw again the next day. "This one only did 4 trees in an hour."
The salesman takes the chainsaw back and showed the man another one.
"OK, this is our best chainsaw. 60 Trees in an hour!"

The man takes the chainsaw and leaves.

The next day he comes back very frustrated. "This one is just as bad. I could only cut down 6 trees in the hour."

The sales man was very concerned as these were their best saws. "Well, let me give it a try." He took the chainsaw and pulled the cord and the chainsaw roared to life.
The man jumped back startled and exclaimed "What is that sound!?!?!"