As a person looking for a sitter in my home I definitely wouldn't contact anyone who hadn't bothered to get the simple background check.

I'm hesitant to post this because it's not a story with a happy ending. There's lots of information out there about mast cell tumors, so you've probably already read plenty of terrible things. Anyway, you asked and I have experienced it, so here's a short version of our story.

At age 14 our dog got a cyst on her shoulder. We had it removed and it came back as a mast cell tumor within a few months. We had the tumor removed with the understanding that it was a temporary comfort thing and would give us some time to play with her as a healthy dog. We had to put her down within a couple of months of the surgery, but we did get one last really fun month with her. Looking back, I don't regret a day with her but I'm not convinced surgery was the right thing.

I hope you're lucky and your pup's tumors are the least aggressive.