Why become a better salesman without commission?

As a salesman/maintenance man at an unnamed company, a small family-owned business, I'm having a bit of a dilemma. I feel the need to work on my salesmanship skills for my job, but my wife, also a co-worker, is of the opinion that this doesn't matter much, seeing as we don't receive any commission.

My main question is: what is the incentive, if any, for improving my salesmanship abilities in a job where it doesn't seem to make any difference? Am I simply wasting my time?