listers.in uses a popular HTML editor called CKEditor for item description. CKEditor creates clean and standards-compliant html code. It removes/changes dirty html code automatically.
But sometimes auto-formatting is unwanted feature for sellers because they already have original html templates for their item description. You can disable the HTML editor from settings page if you don’t want to use it.
A plain <textarea> field will be used for item description when you disabled the HTML editor. <textarea> will not remove/change your original html code at all!