> The paper also is riddled with spelling and grammar mistakes, and while that doesn't have anything to do with the science, it does say something about the sloppiness of the researcher, I think.

I have reviewed many papers that were originally quite badly written, but were not bad papers at all. Many non-native speakers are bad at English, so they rely on some external editing service, and they do not want to pay this service until the paper has been properly reviewed and they have made the proposed changes. Of course it does not send a good signal, but the content of the article should not be judged in basis to that.