I am looking for a reliable professional editing service where I can get my papers reviewed. Searching google returns gazillion options but its very hard to determine which one is truly professional and worth spending money on. What should I look for in evaluating services in order to sort the wheat from the chaff?
I would suggest looking for professional editors associations in your country. Here in Canada, for example, we have the Editors Association of Canada. Such associations will likely have referral services and perhaps certification programs. Membership in a professional society is usually a plus in evaluating any service provider. (Not sufficient in itself, but a good sign.) Most associations have code of conduct and practice. Some require proof of experience and/or competence to join or to achieve full membership. And there mere fact that the person is willing to pay their dues says that they are somewhat serious about what they are doing.
In the past I have used www.prowritingaid.com for editing creative writing peices and also essays when I was in college and I've found it works well as a free option. It's easy to paste a chunk of text and see what needs some refining based on the reports that are generated. This isn't the same as a human person giving feedback, but it does provide helpful information. Hope this helps.