Once the manuscript does say what is intended, and says it well, then I give it a good copy edit, to make sure that the grammar and spelling are correct.
One note about grammar: Once the basics have been rectified, such as nouns agreeing with verbs and commas used judiciously, what is correct grammar becomes a matter of opinion. The Chicago Manual of Style is the grammar Bible for many publishers and editors. However, there are other equally valid standards. I use the standard my client and his publisher want to see.