As said above, copyscape to confirm it is unique, some sort of readability software such as some others have listed above. I dont know how well they work but I know for example that you get tools for wordpress that tell you the Flesch score of content which is supposed to dictate how readable and simple it is to understand so I am assuming it is possible to some extent. Even at the very least, I guess Google for example would know if there were words that very rarely appear together and other indicators that text is spun, so I am guessing some tools can do the same sort of thing.
The other option of course is to read it yourself, or even pay someone to read - for example if you spin 100 articles, then just take 1 or 2 of them and get them proof read - that would give you a reasonable indication of what the rest are going to be like.
Or as stated above, pay for the articles instead - you can get reasonable content here for like $1/300 words for example.