Being a service person: Dealing with customers' disagreements

I’ve mentioned before on this board my experiences as a gardener, but one things really irks me. Disagreement between customers.
Specifically, yesterday morning I went to move some used wood for an older married couple in Torrance–I’ll call them Giuseppe and Linda Custodio (they’re Filipino).
Linda–several times a grandmother–slipped into a narrow space between a shed and the outside fence and had me trundle some planks–2x4"s and 4x4"s, mostly–over across the backyard to a narrow space at the end of the roof where I could slide them into the space and Linda would drag them onto a stack.
But this morning, when I went there to do weeding in the back, Giuseppe angrily told her that we had done this without his consent and Linda, with an irritated sigh, told me we’ll have to put them back in the back of the yard… We did so.
I have rarely had to deal with customers disagreeing like this, and Lord knows I have no place trying to settle the argument myself.
Any comments?

Move their planks wherever they want and then charge them extra for it.