Proofreading is key to define the impact of your copy. You should always rely on a professional proof-reader to check your copies for potential grammar or syntax mistakes but also to ensure that the style is fluid and adequate (tone, register, cohesion, clarity).
The proof-reader works on the text to make it sound more natural, pleasant to read, effective, and correct. Nothing makes a worse impression than a poorly structured or misspelled text.
Do you want your customers to trust you? Then you need to aim for the right style to connect with them and prove that you speak their language.