I've only once been handed a cracked racquet. If it still had strings in it, I would have suggested he leave it as was. In this instance he'd broken a string, so effectively the racquet was useless to him in the current state. Before starting, we agreed:
- I would not be liable for any further damage done
- I would be paid regardless of the outcome
- We would use a low tension
It's worth noting that in my case it was someone I knew pretty well, and so I sympathised more with him. Had it been a stranger, I probably would have declined.
I also decided I should wear some form of eye protection just in case. Only time I've ever strung in sunglasses.