Of course, after each completed transaction you can rate the user who bought the item from you. You can give him/her a star rating on a scale of 1 to 5 and add a comment to the rating.
Remember that the other side of the transaction can reply to your rating.
In LESS_ you can not delete received or submitted ratings by yourself. If for any reason you do not agree with a rating you have received, you can let us know by writing to firstname.lastname@example.org