Pooping in front of you can be an extreme marking behavior called middening. The animal wants to make it very clear he's uncomfortable with you entering his space. I've only had one dog do it as I entered his playroom, but you'll see it all the time in multi-cat homes. In my case, the dog was fine once the owner was gone and he didn't feel he had to guard her. But trust your instincts. It's better to refuse a booking than get stuck in a situation with an unhappy animal.