K.B.
My husband owns a landscape construction company and tips are not customary. On occasion, a customer will give him a giftcard for Christmas or at the end of a VERY LARGE project. It is not expected at all. If he is working really late or doing a large job, customers will occasionally buy pizza for him and his crew. Or, if it is really hot outside, sometimes customers will bring drinks out to them. None of it is expected, definitely not customary- he has been doing this for over 15 years.
ETA: As someone else said- pay your bill promptly and that is tip enough! Bill collecting is my husband's absolute least favorite thing about his job.