I rarely do repeats, though I appreciate the sentiment behind such offers. I get a lot of them, but prefer variety. I don’t mind helping folks out, though — within reason — even if I never see them again. To me, that goes beyond sitting, to life in general.
Of course that’s at my discretion. And I wouldn’t let entitled people take advantage of me. But I’ve not found that to be an issue — I can be firm with boundaries as needed.
Of course with sitting, I always figure it’s better to vet carefully and catch a potentially bad dynamic or tone as early as possible, starting with the listing. Personally, I’d prefer to miss a sit over a false negative than risk a bad sit by ignoring warning signs.
If you end up on a sit with someone who tries to take advantage or treats you like a servant, it can be tough for many folks to push back in ways that avoid friction or bad reviews.