Tutors at WTS don't proofread and they don't edit. They won't make corrections as they read your paper. They will, however, talk with you about how you can improve any aspect of a paper, ranging from punctuation to overall organization—depending on what you ask for. The aim of tutorials at WTS is to make you better able to evaluate your own writing, and to revise it accordingly.
Below is a link to a Word document with a list of paid editors (note: these editors are not employed by WTS):