I agree that some sales pages, (and indeed products themselves), are poorly written and clearly from people whose first language is not English. Sadly there is often a lack of quality presentation in some products written by people whose native tongue is English too!

Recently I have been asked by several people to edit their sales pages/products, correcting grammar, spelling, punctuation so it reads well. It is a service these people can take advantage of if they choose to. They may well be losing follow up sales if their product is poorly presented, no matter how good the content might be.