He asks a boy where he can find a barber and the boy says there are only two barbers in the town.

The boy shows him the first one. Inside the barber has hair all over the floor, dirt everywhere and long uneven hair.

He goes to the other one and sees the barber is dressed in pristine clothing, well cut, and his floors are well swept and clean.

The man changes his mind and goes to the other barber.

Why does he do this?

At the outset, it is known that thre are no other barbers apart form the ones mentioned in the problem text. Let us denote the  barber with the good and even  haircut as A and the barber with imperfect and uneven haircut as B.

Accordingly, A must have received his haircut from B, which goes to show that B is an expert in his profession.
On the other hand, the haircut that B received from A was shabby and uneven, which implies that B is not fully skilled at his profession.

Consequently, it is quite natural for the man to go and receive his haircut from B, who is certainly the skilled barber. 

Nice Puzzle.