The person you choose to look over your statement should be checking everything. Along with grammar and spelling errors they should check the tone of the paper, the flow of the paper, and the overall style of the paper. So, it makes sense that the person you choose to look over your admission essay should be well tuned in writing. Additionally, they should also be able to let you know if there is anything they feel you should omit or add. Once you have made the changes they recommend, then you should have them re_read your personal statement to ensure quality. If you want to be ultra_safe, then have yet another set of fresh eyeballs look over your revised personal statement.
You already know that your personal statement could be the one factor that keeps you out, or lets you into the school of your dreams, but you may not know how important it is to have a fresh set of eyes on it before you turn it in. While you may have read over your personal statement several times, there are still reasons that you will want someone else to read it over as well.