I used Chicago Cat Nannies and had a decent experience. However there were some issues (sitter showed up late and disorganized for first meeting, and didnt' really spend any time meeting the cats, and I found out later than there were two different people doing the sitting, when I thought it would be only one consistent person, as it says on the website). I posted my experiences on yelp and rated the service 3-stars.
Pros: decent sitters, online blog
Cons: irrational and vindictive owner, service inconsistent with what is advertised
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