Yesterday I had an interesting experience.
I met with a young doctor who was in the process of setting up his own clinic. He'd engaged the services of an engineer who was late in delivering drawings. I made no promises but I told him I'd help him out as best I could. We spent about 30 minutes discussing what I needed to provide him and changes that I suggested that he make to the lighting that the architect had laid out (badly). We concluded the meeting amicably and he was going to have the architect send me electronic drawings.
Half and hour later he showed up with a case of Heineken and an apology for wasting my time.
Now that's a graceful way to reject someone's professional services.