It's only happened a couple of times on incall, one was with a young reg and we changed positions and there was a bit of blood on the condom and it did put him off so we finished the session early and I refunded him a bit of the money. He did book again though at least.
The worst though was on an outcall and a tiny bit was on his bed and he noticed. As it was just a bit I denied it was from period and got a tissue and wiped myself and luckily nothing was on it so I said are you sure it isn't you? Or maybe I've cut myself somewhere else but I can't see.
I did feel bad though and he said he'd just changed the sheets but I said I apologise if it was me.
The mini pill gives me irregular periods so it's hard to plan with it.