If it was a good customer, well priced job, then I would just remove. And I would let them know 'oh there was some cement on the conny, av got that off for ya' im sure they wil be grateful.
I know were running businesses, not charoties, but sometimes it pays to turn an odd favour... A customer of mine who runs a chain of shops, asked me to remove some debris out of a guttee, well, it was at the downspout, one of those old 'hoppers' turns out it was the biggest weed that god invented, I removed it for him and I said 'billy, you dont owe me anything, call it a favour'
On this occasion, the customer has turned into a very good friend, and has helped me out countless times, signed passport forms for me & family (would of cost £100 off a doctor )